GIFT  OF 

ASSOCIATED  ELECTRICAL  AND 
MECHANICAL   ENGINEERS 


MECHANICS  DEPARTMENT 


399 


University  of  California 


THE 

GAS  TURBINE 

PROGRESS    IN    THE    DESIGN    AND    CONSTRUCTION 

OF  TURBINES  OPERATED  BY  GASES 

OF  COMBUSTION 


BY 


HENRY  HARRISON  SUPLEE,  B.Sc. 

MEMBER   OF  THE  AMERICAN    SOCIETY   OF  MECHANICAL   ENGINEERS,   MEMBER    OF    THE    FRANKLIN 

INSTITUTE,  MEMBRE    DE   LA    SOCIETE    DES    INGENIEURS   CIVILS   DE  FRANCE, 

MITGLIED   DES  VEREINES   DEUTSCHER  INGENIEURE. 

AUTHOR    OF 

"THE  MECHANICAL  ENGINEER'S   REFERENCE  BOOK,"  ETC.,  ETC. 


PHILADELPHIA 

J.  B.  LIPPINCOTT  COMPANY 

1910 


A1 


Engineering 
Library 

COPYRIGHT,  1910 
BY  J.  B.  LIPPINCOTT  COMPANY 


Printed  by  J.  B.  Lippincott  Company 
The  Washington  Square  Press,  Philadelphia,   U.  S.  A. 


PREFACE 

THIS  volume  is  intended  to  place  in  the  hands  of  engi- 
neers and  experimenters  such  theoretical  and  practical  data 
as  are  now  available  in  the  solution  of  the  problem  of  the 
gas  turbine. 

At  the  present  time  such  machines  are  yet  in  the  experi- 
mental stage,  and  it  is  still  uncertain  to  what  extent  they 
may  become  generally  practicable.  There  has,  however,  been 
expended  much  study  and  effort,  both  in  the  investigation  of 
the  theoretical  principles  upon  which  the  gas  turbine  depends, 
and  in  the  construction  of  machines  intended  to  realize,  more 
or  less  effectively,  the  possibilities  which  have  been  indicated 
/by  such  studies. 

Much  of  the  information  contained  in  this  book  is  included 
in  the  transactions  of  learned  societies,  in  the  pages  of  peri- 
odicals, and  in  the  records  of  private  experimenters,  and  it  is 
believed  that  by  gathering  in  one  volume  the  results  of  the 
work  of  English,  French,  German,  and  other  organizations, 
the  engineers  and  mechanics  who  are  investigating  the  sub- 
ject may  be  assisted  by  perceiving  what  has  already  been 
accomplished,  and  thus  avoid  unnecessary  repetition  of 
work  which  is  already  on  record. 

The  gas  turbine  need  not  be  a  machine  of  exceedingly 
high  thermal  efficiency  in  order  to  be  available  for  many 
purposes.  The  advantages  accompanying  a  continuous  turn- 
ing effort,  instead  of  the  intermittent  impulses  of  the  recip- 
rocating gas  or  gasoline  motor,  may,  in  many  instances,  over- 
balance a  somewhat  lower  fuel  economy;  while  the  reduction 
in  weight,  consequent  upon  the  attainment  of  a  very  high 
rotative  speed,  may  become  of  controlling  importance.  It  is 
therefore  of  the  utmost  desirability  that  all  the  conditions  be 

i 


PREFACE 


taken  into  account,  and  it  is  for  this  purpose  that  the  present 
volume  has  been  prepared,  collecting  together  the  relative 
influence  of  the  various  elements  of  which  the  problem  is 
composed. 

The  author  desires  to  acknowledge  the  assistance  which 
has  been  freely  rendered  to  him  in  the  preparation  of  this 
volume.  To  the  memory  of  his  colleague  in  the  Societe  des 
Ingenieurs  Civils  de  France,  M.  Rene  Armengaud,  he  records 
his  obligations  for  personal  communications  describing  the 
experimental  work  conducted  in  the  laboratory  at  St.  Denis; 
and  to  M.  Alfred  Barbezat  he  desires  to  express  his  apprecia- 
tion for  the  continuation  of  this  most  important  work.  To 
M.  Armand  de  Dax,  Secretaire  Administratif  of  the  Societe 
des  Ingenieurs  Civils  de  France,  and  to  M.  L.  Sekutowicz,  his 
colleague  in  the  Societe,  he  acknowledges  the  kind  permission 
to  translate  the  important  paper  of  the  latter  author;  and  to 
Mr.  Edgar  Worthington,  Secretary  of  the  Institution  of 
Mechanical  Engineers  (London)  as  well  as  to  the  author,  Mr. 
R.  M.  Neilson,  he  is  indebted  for  permission  to  reproduce  the 
paper  of  the  latter,  as  well  as  the  discussion  which  it  elicited. 
The  writer  also  wishes  to  express  his  indebtedness  to  Dr.  San- 
ford  A.  Moss,  Dr.  Charles  E.  Lucke,  Prof.  Sidney  A.  Reeve, 
Prof.  Lionel  S.  Marks,  and  Dr.  H.  N.  Davis,  for  valued  sug- 
gestions and  assistance. 

HENRY  HARRISON  SUPLEE. 

NEW  YORK,  November,  1909 


CONTENTS 


PAGE 

INTRODUCTION 5 

CHAPTER  I. 

HISTORICAL .       9 

The  Smoke  Jack,  the  First  Gas  Turbine;  Barber's  Turbine;  Ferni- 
hough's  Patent;  Burdin's  Experiments;  Tournaire's  Communication 
to  the  French  Academy;  Bourne's  Suggestions;  Boulton's  Patents; 
the  Stolze  Hot- Air  Turbine;  Parsons's  Patent;  Laval,  Lemale,  Armen- 
gaud;  Later  Papers. 

CHAPTER  II. 

THE  DISCUSSION  BEFORE  THE  INSTITUTION  OF  MECHANICAL  ENGINEERS.  28 
Paper  by  R.  M.  Neilson,  Discussing  Various  Available  Cycles  and 
their  Merits  and  Disadvantages;  Discussions  by  Messrs.  Henry 
Davey,  F.  W.  Burstall,  James  Atkinson,  Col.  R.  E.  B.  Crompton,  H. 
M.  Martin,  Robert  H.  Smith,  and  Mr.  Neilson.  Communications 
from  Dugald  Clerk,  W.  J.  A.  London,  E.  Kilburn  Scott,  and  George 
A.  Wigley. 

CHAPTER  III. 

THE  DISCUSSION  BEFORE  THE  SOCIETY  OF  CIVIL  ENGINEERS  OF  FRANCE.   108 
Paper  by  M.  L.  Sekutowicz,  Treating  of  the  Mechanical  and  Ther- 
modynamic  Efficiencies  of  the  Gas  Turbine,  the  Various  Cycles  and 
the  General  Details  of  Construction. 

CHAPTER  IV. 

THE  DISCUSSION  BEFORE  THE  SOCIETY  OF  CIVIL  ENGINEERS  OF  FRANCE 

(Continued) 219 

Comments  on  the  Paper  of  M.  Sekutowicz  by  MM.  Armengaud,  Rey, 
Hart,  Bochet,  and  Letombe. 

CHAPTER  V. 

ACTUAL  BEHAVIOR  OF  GASES  IN  NOZZLES 222 

Experiments  of  Dr.  Charles  E.  Lucke;  Table  of  Temperature  Drop 
with  Compressed  Air  in  the  Laval  Turbine;  Trials  of  Turbines  at  St. 
Denis;  Desirability  of  Further  Experiments. 

iii 


iv  CONTENTS 


CHAPTER  VI. 

THE  PRACTICAL  WORK  OF  ARMENGAUD  AND  LEMALE 227 

The  Explosion  Gas  Turbine;  the  Combustion  Turbine;  the  Original 
Experimental  Machine  at  St.  Denis;  Details  of  Combustion  Chamber; 
Structural  Arrangement  of  Parts;  the  Rateau  Polycellular  Air  Com- 
pressor; the  300  Horse-Power  Gas  Turbine;  Gas  Turbines  in  Subma- 
rine Torpedoes;  Data  and  Results  of  Tests;  the  Karavodine  Turbine. 

CHAPTER  VII. 

GENERAL  CONCLUSIONS 251 

INDEX .  255 


THE  GAS  TURBINE 


INTRODUCTION. 

ALTHOUGH  the  gas  turbine  was  one  of  the  earliest  forms 
of  combustion  motor  it  failed  to  attain  practical  or  com- 
mercial importance,  and  it  is  only  since  the  steam  turbine 
has  reached  its  present  commanding  position  that  the  possi- 
bility of  developing  the  gas  turbine  in  similar  manner  has 
been  seriously  considered. 

The  practical  difficulties  in  the  way  of  the  realization 
of  a  successful  gas  turbine  are  very  great.  The  high  tem- 
peratures involved  demand  especial  care  in  order  that  the 
strength  of  the  material  may  not  be  unduly  affected.  The 
high  rotative  speeds  required,  if  high  efficiencies  are  to 
be  secured,  render  the  mechanical  problems  connected  with 
centrifugal  action  more  serious  even  than  with  the  steam 
turbine;  while  the  doubt  as  to  the  action  of  hot  gases  in 
diverging  nozzles  renders  an  important  element  in  the 
theory  yet  uncertain. 

At  the  same  time  there  has  been  going  on,  during  the 
past  few  years,  in  Europe  and  in  America,  some  very  effec- 
tive experimental  work  upon  the  gas  turbine;  while  the 
theory  has  also  been  made  the  subject  of  elaborate  study 
by  English,  French,  German,  and  American  scientists. 

Most  of  the  information  regarding  this  work  is  in  a  form 
unavailable  for  the  practical  engineer  and  investigator. 
The  theoretical  discussions  are,  for  the  most  part,  contained 
in  the  transactions  of  professional  societies;  much  of  it  in 
languages  other  than  English.  The  practical  experiments 

5 


GAS  TURBINE. 


are  being  conducted  behind  closed  doors  and  reliable  infor- 
mation is  not  generally  attainable  in  detailed  form. 

It  has  therefore  been  thought  desirable  to  gather  under 
one  cover  the  most  important  papers  which  have  appeared 
upon  the  subject  of  the  gas  turbine  in  England,  France, 
Germany,  and  Switzerland,  together  with  some  account 
of  the  work  in  America,  and  to  add  to  this  such  information 
upon  actual  experimental  machines  as  can  be  secured. 


FIG.  1. — Scheme  of  gas  turbine  with  reciprocating  compressor. 

In  the  present  state  of  the  art  this  is  all  that  can  be  done, 
but  it  is  believed  that  this  will  aid  materially  in  the  conduct 
of  subsequent  work,  and  place  in  the  hands  of  the  gas-power 
engineer  a  collection  of  material  not  generally  accessible 
or  available  in  convenient  form. 

The  general  lines  along  which  the  plans  of  the  various 
gas  turbines,  now  under  experimental  investigation,  are  con- 


THE   GAS   TURBINE. 


structed,  will  be  understood  from  the  accompanying  sche- 
matic diagram.  This  is  substantially  as  given  by  Dr.  Sanford 
A.  Moss  in  connection  with  his  thesis  upon  the  gas  turbine 
presented  to  the  faculty  of  Cornell  University  in  1903. 

The  fuel,  in  this  case  some  form  of  liquid  hydrocarbon, 
is  forced  into  a  combustion  chamber,  together  with  the 
proper  amount  of  compressed  air  for  its  combustion.  The 
products  of  combustion  are  discharged  through  a  diverg- 


CombusElon  Chamber 


Air 
Inlet 

LJ 

Compressor 

Turbine  &  I 

Exhaust 

FIG.  2. — Scheme  of  gas  turbine  with  multiple  wheels  and  rotary  compressor. 

ing  nozzle  upon  the  buckets  of  an  impulse  wheel  which  is 
thus  caused  to  rotate,  a  portion  of  the  power  developed 
being  used  to  drive  the  compressor,  and  the  remainder  being 
available  for  external  use. 

Since  one  of  the  presumed  advantages  of  the  gas  turbine 
over  the  ordinary  gas  engine  is  the  substitution  of  continu- 
ous rotary  motion  for  the  reciprocating  action  of  a  piston 
in  a  cylinder,  it  is  undoubtedly  desirable  that  a  rotary  com- 
pressor be  used,  so  that  the  reciprocating  pump  may  be 


8  THE   GAS   TURBINE. 

dispensed  with.  The  general  arrangement  of  such  an  appa- 
ratus, including  also  a  multistage  turbine,  is  here  given,  as 
devised  by  Mr.  Rudolf  Barkow  (Fig.  2). 

Here  the  air  is  drawn  in  and  compressed  by  a  rotary 
compressor,  mounted  on  a  continuation  of  the  turbine  shaft. 
The  compressed  air  is  delivered  to  the  combustion  chamber, 
into  which  the  liquid  fuel  is  also  injected,  and  the  combustion 
takes  place  under  pressure,  the  gases  and  products  of  com- 
bustion passing  through  the  diverging  nozzle  to  the  buckets 
and  guide  vanes  of  the  turbine. 

The  extent  to  which  these  schematic  forms  have  been 
developed  from  the  earliest  beginnings,  and  the  lines  along 
which  theory  and  experiment  have  been  pushed,  will  be 
seen  in  the  following  pages. 


CHAPTER  I. 

* 

HISTORICAL. 

THE  use  of  the  expansive  action  of  heat  upon  elastic  gases 
to  operate  a  revolving  wheel  for  the  production  of  power 
is  by  no  means  recent;  in  fact  it  antedates  the  employ- 
ment of  a  piston  reciprocating  in  a  cylinder  for  the  same 
purpose.  Considered  in  this  broad  sense  there  is  no  doubt 
that  the  windmill  is  entitled  to  be  called  a  gas  turbine,  since 
the  pressure  of  the  moving  air  upon  its  sails  can  be  traced 
to  'the  currents  produced  by  changes  of  temperature  in  the 
atmosphere. 

Leaving  aside  the  windmill,  however,  there  can  be  little 
question  as  to  the  claims  of  the  mediaeval  "Smokejack" 
to  be  considered  as  a  gas  turbine.  This  machine,  the  origin 
of  which  it  is  impossible  to  trace,  has  been  attributed  to 
Leonardo  da  Vinci  and  illustrations  of  it  are  to  be  found 
in  his  engineering  sketch  books.  A  somewhat  later  form  is 
shown  in  the  illustration,  this  being  taken  from  an  engraving 
in  Bishop  Wilkins's  book  "  Mathematical  Magick,"  published 
in  1648,  the  present  engraving  and  following  description 
being  found  in  the  edition  of  1680. 

After  referring  to  the  action  of  windmills  and  to  Eolipiles, 
the  learned  bishop  continues:  "But  there  is  a  better  inven- 
tion to  this  purpose  mentioned  in  Cardan,*  whereby  a  spit 
may  be  turned  (without  the  help  of  weights)  by  the  motion 
of  the  air  that  ascends  the  Chimney;  and  it  may  be  useful 
for  the  roasting  of  many  or  great  joynts  :  for  as  the  fire 
must  be  increased  according  to  the  quantity  of  meat,  so 
the  force  of  the  instrument  will  be  augmented  proportionably 
to  the  fire.  In  which  contrivance  there  are  these  conveni- 
ences above  the  Jacks  of  ordinary  use  : 

*  Cardan.    De  Variet.  Rerum.  I.  12,  c.  58. 


10 


THE   GAS   TURBINE. 


"1.  It  makes  little  or  no  noise  in  the  motion. 

"2.  It  needs  no  winding  up,  but  will  constantly  move  of 
itself,  while  there  is  any  fire  to  rarifie  the  air. 

"3.  It  is  much  cheaper  than  the  other  instruments  that 
are  commonly  used  to  this  purpose.  There  being  required 
with  it  only  a  pair  of  sails,  which  must  be  placed  in  that 
part  of  the  Chimney  where  it  begins  to  be  straightened,  and 
one  wheel,  to  the  axis  of  which  the  spit  line  must  be  fastened, 
according  to  the  following  Diagram. 


FIG.  3. — The  smoke  jack.    The  first  gas  turbine.    From  Bishop  Wilkins's  "Mathematical 

Magick,"  1680. 

"The  motion  to  these  sails  may  likewise  be  serviceable 
for  sundry  other  purposes,  besides  the  turning  of  a  spit, 
for  the  chiming  of  bells  or  other  musical  devices;  and  there 
cannot  be  any  more  pleasant  contrivance  for  continual  and 


THE   GAS  TURBINE.  11 

•cheap  music.  It  may  be  useful  also  for  the  reeling  of  yarn, 
the  rocking  of  a  cradle  with  divers  the  like  demestick  occa- 
sions. For  (as  was  said  before)  any  constant  motion  being 
given,  it  is  easie  for  an  ingenious  artificer  to  apply  it  unto 
various  services. 

"These  sails  will  always  move  both  day  and  night,  if 
there  is  but  any  fire  under  them,  and  sometimes  though 
there  be  none.  For  if  the  air  without  be  much  colder  than 
that  within  the  room,  then  must  this  which  is  more  warm 
and  rarefied,  naturally  ascend  through  the  chimney,  to  give 
place  unto  the  more  condensed  and  heavy,  which  does 
usually  blow  in  at  every  chink  or  cranny,  as  experience 
shews." 

After  the  smoke  jack,  the  next  proposition  for  a  gas 
turbine  appears  to  be  that  of  Barber,  who  took  out  a  British 
patent  in  1791,  No.  1833,  which  seems  like  a  very  complete 
.anticipation  of  nearly  all  the  most  recent  developments  in 
this  line.  Barber's  patent  includes  the  distillation  of  the 
gas  from  wood,  coal,  or  oil,  its  delivery,  with  the  proper 
amount  of  air  into  a  combustion  chamber,  and  the  discharge 
of  the  products  of  combustion  upon  the  buckets  of  a  turbine 
wheel. 

He  even  went  so  far  as  to  inject  water  into  the  combus- 
tion chambers  to  reduce  the  temperature,  the  mixed  steam 
and  gases  acting  upon  the  wheel. 

The  illustration,  Fig.  4,  gives  an  idea  of  Barber's  patent. 

The  vessels  marked  1,  1,  are  retorts  for  the  production 
of  the  gas  to  be  used,  these  being  intended  for  the  distilla- 
tion of  coal,  wood,  etc.,  by  means  of  an  external  flame. 
When  it  is  remembered  that  Murdock  did  not  begin  his 
experimental  investigations  into  the  manufacture  of  coal 
gas  until  1792,  one  year  after  Barber's  patent,  and  only 
made  his  results  public  in  1797,  it  will  be  seen  that  Barber 
was  distinctly  in  advance  of  his  time.  The  retorts  shown 
in  Barber's  drawing  are  in  duplicate,  for  alternate  charging 


12 


THE   GAS   TURBINE. 


FIG.  4. — Barber's  gas  turbine,  1791. 


and  discharging,  the'  gas  being  delivered  into  a  cooling 
chamber  B,  from  which  it  is  drawn  by  one  of  the  compres- 
sing pumps  C,  D,  and  delivered  to  the  receiver  4,  from 
which  it  passes  to  the  triangular-shaped  combustion  cham- 


THE   GAS   TURBINE. 


13 


bers.  The  other  compressing  pump  delivers  air  and  vapor 
of  water  into  the  combustion  chamber,  and  the  products 
of  combustion  are  discharged  upon  the  buckets  of  the  wheel 
to  effect  its  rotation.  The  drawing  shows  the  reducing 
gearing  for  operation  of  the  compression  pumps,  the  power 
to  be  taken  from  the  upper  gear  shaft. 

It  is  evident  that  Barber's  machine  involved  construc- 
tive problems  altogether  unsolved  in  his  time,  but  the  appa- 
ratus was  surprisingly  complete  in  its  conception,  including 
combustion  at  constant  pressure,  with  pumps  for  the  supply 
of  air  and  fuel,  together  with  the  use  of  vapor  of  water  for 
the  reduction  of  temperature,  and  a  train  of  gear  wheels 
for  the  reduction  of  the  speed. 


FIG.  5. — Fernihough's  turbine,  1850. 

Nothing  seems  to  have  been  done  for  more  than  fifty 
years  after  the  patent  of  Barber,  but  in  1850  a  mixed  steam 
and  gas  turbine  was  proposed  by  W.  F.  Fernihough,  and 
patented  in  Great  Britain,  No.  1328,  of  1850.  This  appa- 
ratus, Fig.  5,  consisted  of  a  chamber  A,  lined  with  refractory 
material,  and  fitted  with  a  grate  B,  on  which  the  fuel  was 


14  THE   GAS   TURBINE. 

ignited.  Air  was  supplied  under  pressure  through  E,  while- 
water  was  sprayed  from  above  at  H,  and  the  mixture  of 
steam  and  the  gases  of  combustion  were  delivered  through 
the  nozzle  I  upon  the  wheel  L,  L. 

In  the  mean  time  Burdin,  in  France,  had  proposed,  in 
1847,  to  make  a  hot-air  turbine,  using  a  multiple-wheel 
rotary  compressor  to  deliver  air  through  a  heating  chamber 
to  a  corresponding  rotary  motor.  This  plan  was  included 
in  the  remarkable  communication  of  Tournaire,  presented 
to  the  Academic  des  Sciences  in  1853.  The  original  memoir 
of  Tournaire  is  remarkable  in  many  ways,  both  for  the 
breadth  of  its  conception  of  the  problem,  and  also  because 
it  refers  to  "  elastic  fluid  turbines,"  not  limiting  the  action 
to  steam,  but  including  hot  air  and  gases,  and  thus  distinctly 
including  the  gas  turbine.  In  view  of  the  importance  of 
this  communication  it  is  here  translated  entire,  from  the 
Compte  Rendu  des  Seances  de  V Academic  des  Sciences  of 
March  28,  1853,  pp.  588-593. 

"APPLIED  MECHANICS. — Note  upon  multiple  and  succes- 
sive-reaction turbine  devices  for  the  utilization  of  the  motive 
power  developed  by  elastic  fluids;  by  M.  Tournaire,  Ingenieur 
des  Mines.  Commission:  MM.  Poncelet,  Lame,  Morin, 
Combes,  Seguier: 

"  Numerous  attempts  have  been  made  to  cause  the  vapor 
of  water  or  other  gaseous  substances  to  act  by  reaction  upon 
the  blades  or  passages  of  rotative  apparatus  similar  to  tur- 
bines or  other  hydraulic  wheels;  but  down  to  the  present 
time  these  inventions  have  not  been  crowned  with  practical 
success.  The  economical  application  of  the  principle  of 
reaction  to  machines  operated  by  elastic  fluids  would  never- 
theless be  of  a  very  high  degree  of  interest,  since  the  moving 
portions  would  thereby  be  reduced  to  very  small  dimensions, 
and,  in  the  great  majority  of  cases,  the  transmission  of  the 
motion  would  be  lightened  and  simplified.  In  a  word,  such 
machines  would  enable  the  same  advantages  to  be  realized 


THE   GAS   TURBINE. 15 

as  are  found  with  hydraulic  turbines  compared  with  water- 
wheels  of  large  diameter. 

"  Elastic  fluids  acquire  enormous  velocities,  even  under 
the  influence  of  comparatively  low  pressures.  In  order  to 
utilize  these  pressures  advantageously  upon  simple  wheels 
analogous  to  hydraulic  turbines,  it  would  be  necessary  to  per- 
mit a  rotative  motion  of  extraordinary  rapidity,  and  to  use 
extremely  minute  orifices,  even  for  a  large  expenditure  of  fluid. 
These  difficulties  may  be  avoided  by  causing  the  steam  or 
gas  to  lose  its  pressure,  either  in  a  gradual  and  continuous 
manner,  or  by  successive  fractions,  making  it  react  several 
times  upon  the  blades  of  conveniently  arranged  turbines. 

1  'We  must  attribute  the  origin  of  the  researches  which 
we  have  made  upon  this  subject  to  the  communications 
which  M.  Burdin,  Ingenieur  en  Chef  des  Mines,  and  membre 
Correspondant  de  I'lnstitut,  has  had  the  courtesy  to  make 
to  us,  and  which  go  back  to  the  close  of  1847.  M.  Burdin, 
who  was  then  engaged  upon  a  machine  operated  by  hot 
air,  desired  to  discharge  the  compressed  and  heated  fluid 
upon  a  series  of  turbines  fixed  upon  the  same  axis.  Each 
one  of  these  wheels  was  placed  in  a  closed  chamber,  the  air 
to  be  delivered  through  injector  nozzles  and  discharged 
at  a  very  low  velocity.  The  author  proposed  to  compress 
the  cold  air  by  means  of  a  series  of  blowers  arranged  in  a 
similar  manner.  This  idea  of  employing  a  number  of  suc- 
cessive turbines  in  order  to  utilize  the  tension  of  the  fluid 
a  number  of  times  seemed  to  us  a  simple  and  fertile  one; 
we  perceived  in  it  the  means  of  applying  the  principle  of 
reaction  to  steam  and  air  engines. 

"Since  the  differences  in  pressure,  as  used  in  steam 
engines,  are  considerable,  it  became  evident  that  a  large 
number  of  turbines  would  be  required  to  give  a  sufficient 
reduction  in  the  velocity  of  the  fluid  jet.  The  lightness  and 
small  dimensions  of  the  moving  parts  permits  of  very  high 
rotative  speeds  compared  with  those  of  ordinary  engines. 


16  THE    GAS   TURBINE. 

"  Notwithstanding  the  multiplicity  of  parts,  it  is  essential 
that  the  apparatus  should  be  simple  in  its  action,  susceptible 
of  a  high  degree  of  precision,  and  that  adjustments  and 
repairs  should  be  readily  made.  We  believe  that  we  have 
fulfilled  these  essential  conditions  by  means  of  the  following 
arrangements : 

"A  machine  is  composed  of  several  independent  motor 
axes,  connected  by  means  of  pinions  to  a  single  wheel  for 
the  transmission  of  the  motion.  Each  of  these  axes  carries 
several  turbines;  these  receive. and  discharge  the  fluid  at 
the  same  distance  from  the  axis. 

"  Between  two  turbines  is  placed  a  fixed  ring  of  guide 
blades.  The  guides  receive  the  discharge  from  one  reaction 
wheel  and  give  to  it  a  direction  and  velocity  suitable  to 
act  upon  the  following  wheel.  Each  of  these  systems  of 
fixed  and  moving  organs  is  to  be  enclosed  in  a  cylindrical 
case.  The  guide  blades  will  form  portions  of  rings  or  annular 
pieces  placed  in  the  fixed  cylinder,  and  these  should  be  fitted 
very  exactly  the  one  to  the  other.  The  turbines  should  also 
have  the  form  of  rings,  and  should  be  fitted  to  a  sleeve 
attached  to  the  shaft.  Projections  fitting  into  grooves 
secure  the  guides  to  the  cylindrical  case,  and  fasten  the 
turbines  to  the  shaft.  The  first  set  of  guides,  which  act 
simply  as  injector  nozzles,  may  be  made  in  one  solid  piece, 
carrying  the  journal  of  the  shaft.  Nothing  could  be  easier 
than  to  erect  or  dismount  such  an  apparatus.  In  order  to 
transmit  the  motion  it  is  necessary  that  the  shaft  should 
pass  through  the  end  of  the  cylindrical  case  through  an 
opening  fitted  with  a  tight  packing;  such  a  single  stuffing 
box  will  answer  for  each  series  of  reaction  wheels. 

"  After  having  acted  upon  the  turbines  on  the  first  shaft, 
and  thus  parted  with  more  or  less  of  its  elasticity,  the  fluid 
is  caused  to  act  upon  the  turbines  of  the  second  series,  and 
so  on.  For  this  purpose  large  openings  connect  the  end  of 
each  case  with  the  beginning  of  the  one  which  follows. 


THE   GAS   TURBINE.  17 

These  cases  and  passages  may  form  portions  of  the  same 
casting.  Since  the  steam  or  gas  expands  in  proportion  to 
its  passage  through  the  blades  of  the  turbines  and  the 
guides,  it  is  necessary  that  these  blades  should  offer  pas- 
sages of  continually  increasing  size,  and  the  last  portions 
of  the  apparatus  will  have  much  greater  dimensions  than 
the  first. 

uAs  in  the  case  of  hydraulic  reaction  wheels,  the  last 
turbine  on  each  shaft  should  discharge  the  fluid  with  a  very 
low  velocity.  At  its  flow  from  the  other  turbines  the  fluid 
should  have  a  velocity  best  adapted  to  its  entrance  into  the 
passages  between  the  guide  blades.  The  motive  power 
developed  by  these  wheels  will  be  produced,  in  great  part, 
not  by  the  extinction  of  the  actual  velocity  of  the  fluid,  but 
from  the  differences  in  pressures  in  entering  and  leaving 
the  blades.  This  difference  in  pressures  will  produce  a  great 
excess  in  the  relative  velocity  of  discharge  over  the  relative 
velocity  of  entrance,  and,  in  order  that  this  effect  may  be 
obtained,  it  will  suffice,  by  reason  of  the  continuity  of  the 
motion,  for  the  orifices  of  discharge  of  the  passages  to  be 
of  smaller  area  than  the  entrance  orifices;  this  corresponds, 
in  general,  to  the  arrangement  in  most  hydraulic  turbines. 
Considered  with  regard  to  the  relative  velocity  of  rotation, 
the  velocity  of  flow  through  the  passages  of  our  turbines 
will  be  much  greater  than  in  the  passages  in  ordinary  reac- 
tion wheels,  and,  in  consequence,  they  will  be  capable  of 
utilizing  a  much  greater  proportion  of  motive  power. 

uAs  is  the  case  in  all  kinds  of  machinery,  there  are  many 
causes  tending  to  dimmish  the  useful  effect  of  our  apparatus, 
and  to  render  it  lower  than  the  theoretical  effect. 

"One  portion  of  the  fluid  will  escape  through  the  clear- 
ance intervals  which  must  be  left  between  the  fixed  and 
moving  portions,  and  will  have  no  effect  upon  the  turbines 
and  will  not  be  directed  by  the  guide  blades.  There  will  be 
produced  shocks  and  eddies  at  the  entrance  and  discharge 
2 


18  THE   GAS   TURBINE. 

of  the  buckets.  The  considerable  friction,  due  to  the  narrow- 
ness of  the  passages,  will  absorb  a  considerable  portion  of 
the  theoretical  work. 

"All  these  injurious  effects  are  produced  in  hydraulic 
turbines,  some  with  an  intensity  almost  equal  in  degree, 
others,  such  as  the  frictional  resistances,  to  a  much  less 
extent.  These  reaction  wheels  are,  nevertheless,  excellent 
machines.  In  order  that  our  steam  or  hot-air  machines 
should  equal  them  in  respect  to  the  effective  power  utilized, 
a  very  perfect  construction  will  be  necessary,  which  it  will 
perhaps  be  difficult  to  attain,  because  of  the  small  size  of 
the  parts.  But  if  we  consider  the  results  obtained  with 
piston  engines  operated  by  steam  we  see  that  we  may  make 
a  large  allowance  for  losses  before  our  turbines  fail  to  give 
equally  good  results.  Many  of  the  causes  of  loss  inherent 
in  the  use  of  pistons  and  cylinders  will  be  avoided.  Thus, 
the  cooling  effect  due  to  radiation  from  the  exterior  walls 
in  contact  with  the  surrounding  medium  will  become  negli- 
gible, since  our  cylindrical  casings  offer  a  very  small  mass 
and  volume,  traversed  by  a  very  large  flow  of  heat. 

"In  order  that  the  application  of  our  principles  may  be 
successfully  applied  to  engines  operated  by  elastic  fluids 
it  is  necessary  that  great  care  and  a  very  high  degree  of  pre- 
cision be  given  to  the  construction  and  erection  of  the  parts, 
and  that  the  dimensions  and  curves  of  the  blades  be  care- 
fully studied. 

"It  is  necessary  that  the  teeth  of  the  gear  wheels,  which 
are  operated  at  very  high  speeds,  should  run  with  great 
smoothness,  without  shock  or  vibrations;  the  helicoidal 
system  of  gearing  of  White  will  probably  be  found  desirable. 
The  shafts  should  also  be  held  by  outside  collars  in  order 
that  the  metallic  stuffing  boxes  may  not  be  subjected  to 
heavy  pressures.  The  journals  will  receive  the  pressure 
parallel  to  the  axis;  this,  however,  will  be  small,  on  account 
of  the  small  dimensions  of  the  turbines. 


THE   GAS   TURBINE.  19 

11  As  for  the  regulators  of  the  flow  of  the  fluid,  their 
functions  will  be  performed  by  two  slides  or  valves,  one 
placed  in  the  pipe  connecting  the  engine  to  the  generator, 
and  the  other  in  the  opening  through  which  the  exhaust  is 
discharged  into  the  atmosphere. 

"The  principal  advantage  offered  by  the  motors  which 
we  propose  lies  in  the  extreme  lightness  and  small  size  which 
they  offer.  This  is  a  point  upon  which  we  believe  it  unneces- 
sary to  insist  at  length.  The  present  engines  are  too  heavy 
and  cumbersome,  and  are  yet  incapable  of  application  to 
many  purposes  which  are  still  accomplished  by  the  physical 
effort  of  man.  Without  doubt  the  realization  of  our  pro- 
jects would  extend  widely  the  domain  of  mechanical  power. 

11  Applied  to  steam  motors  we  believe  that  our  multiple 
turbines  would  permit  a  reduction  in  the  dimensions  of  the 
reservoirs  or  generators  of  the  fluid;  because,  the  consump- 
tion of  the  motive  material  being  continuous,  the  ebullition 
will  be  effected  very  regularly  in  the  boiler,  and  there  will 
be  much  less  danger  of  the  entrainment  of  a  large  proportion 
of  water.  If  hot  air  be  substituted  for  steam,  as  we  may 
hope  from  the  beautiful  and  fertile  experiments  of  Ericsson, 
our  turbines  will  replace,  very  happily,  the  enormous  cylin- 
ders and  pistons  used  by  the  Swedish  engineer  to  receive 
the  action  of  the  compressed  air.  It  remains  to  be  seen  if 
similar  rotative  apparatus  may  not  be  usefully  employed 
for  the  compression  of  cold  air.  In  case  of  success  a  complete 
mechanical  revolution  will  be  effected  not  only  with  regard 
to  the  quantity  of  combustible  consumed  but  also  in  the 
matter,  not  less  important,  of  the  masses  and  volumes 
which  enter  into  machine  construction." 

It  seems  surprising  that  the  clearly  expressed  ideas  of 
Tournaire  failed  of  immediate  realization,  especially  as 
they  were  passed  in  review  under  the  eyes  of  such  a  com- 
mittee of  mechanical  specialists  as  Morin,  Lame,  and  Ponce- 


20  THE   GAS   TURBINE. 

let;  but  it  is  probable  that  constructive  difficulties,  the 
extent  of  which  was  fully  realized  by  Tournaire,  stood  in 
the  way.  His  work  seemed  to  have  been  almost  entirely 
overlooked  until  recently,  but  there  is  no  doubt  that  he 
fully  grasped  the  problem,  as  the  text  of  his  communication 
to  the  French  Academy  shows. 

At  the  present  time  the  term  " elastic-fluid"  turbine 
appears  in  nearly  all  patent  specifications  for  such  machines, 
their  scope  not  being  limited  to  steam  alone.  Tournaire 
not  only  used  this  very  expression,  but  also  foresaw  the 
application  of  the  multiple-turbine  principle  to  pressure 
blowers  as  well. 

He  further  saw  that  high  fuel  economy,  while  probably 
attainable  with  the  turbine,  was  not  the  only  advantage, 
but  that  material  reduction  in  weight  and  in  bulk  might 
also  be  attained,  points  which  to-day  are  of  even  more 
importance  than  they  were  fifty  years  ago. 

An  interesting  forecast  of  the  practicability  of  the  gas 
turbine  appears  in  the  fifth  edition  of  Bourne's  large  treatise 
on  the  steam  engine,  published  in  1861.  Discussing  the 
advantages  of  superheated  steam,  Mr.  Bourne  says: 

"  Steam  of  a  high  temperature  will,  therefore,  be  more 
economical  in  its  use  than  steam  of  a  lower  temperature, 
and  surcharged  steam  being  much  hotter  than  common 
steam  is  consequently  more  advantageous.  After  all,  how- 
ever, the  temperatures  which  it  is  possible  to  use  with  any 
kind  of  steam  in  an  engine  are  too  low  to  render  any  very 
important  measure  of  economy  possible  by  their  instrumen- 
tality. We  are,  therefore,  driven  to  consider  the  applicability 
of  other  agents,  the  most  suitable  of  which  appears  to  be  air, 
and  this  brings  us  back  to  the  point  from  whence  we  started 
at  the  commencement  of  the  present  chapter.  Small  meas- 
ures of  improvement  are  worth  very  little  consideration 
when  great  and  important  steps  of  progress  are  apparently 
within  our  reach,  and  to  us  it  appears  quite  clear  that  the  prod- 


THE   GAS   TURBINE. 


21 


ucts  of  combustion  may  be  employed  to  produce  motive  power, 
not  through  the  instrumentality  of  a  cylinder  and  piston,  but 
rather  by  means  of  a  turbine  or  an  instrument  like  a  smoke 
jack  or  Barker's  mill,  and  which  may  be  made  to  work  in 
water  or  some  other  liquid.  In  this  way  very  high  tempera- 
tures may  be  dealt  with,  and  it  is  only  by  employing  very 
high  temperatures  that  any  very  great  step  of  improvement 
is  to  be  attained." 


FIG.  6. — Boulton's  multiple  jet  system 

In  1864  the  problem  of  combustion  at  constant  pressure, 
in  connection  with  the  operation  of  a  gas  turbine,  was  inves- 
tigated by  M.  P.  W.  Boulton,  and  his  British  patent,  No. 
1636  of  1864,  contains  some  points  of  interest,  in  the  light 
of  what  has  been  done  since.  He  realized  that  the  high 
velocity  of  the  jet  of  gases  issuing  from  the  nozzle  offered 
a  practical  difficulty,  and  proposed  to  remedy  this  by  the 
use  of  successive  induced  jets  of  increasing  volume  and 
consequently  lower  velocity.  This  is  shown  in  Fig.  4,  the 
gases  being  delivered  through  the  nozzle  A,  inducing  a  cur- 
rent in  B,  and  this  again  in  C.  The  turbine  is  represented 
at  D,  operated  by  the  increased  volume  of  fluid  at  the 
reduced  velocity. 


22 


THE   GAS   TURBINE. 


Another  method  proposed  by  Boulton  for  maintaining 
combustion  at  constant  pressure  is  shown  in  Fig.  7.  The 
gas  is  burned  at  A,  in  a  chamber  C,  under  water,  the  prod- 
ucts of  combustion  passing  up  through  the  water  between 
the  baffle  plates  E,  E,  and  the  mixed  gases  and  steam  being 
delivered  to  the  turbine  from  the  top  of  the  chamber  B. 


FIG.  7. — Boulton's  constant-pressure  combustion  chamber. 

The  idea  of  combustion  at  constant  pressure  to  furnish 
an  elastic  fluid  composed  of  hot  air  and  products  of  com- 
bustion for  use  in  a  turbine  appears  to  have  occupied  the 
attention  of  a  number  of  engineers  from  1870  onward.  John 
Bourne,  the  well-known  British  engineer  and  writer  on  the 
steam  engine,  took  out  two  patents,  one  in  1869  and  the 
other  in  1870,  relating  to  the  combustion  of  coal  dust  for 
the  production  of  gases  for  use  in  a  turbine.  His  plans 
included  the  dilution  of  the  gases  with  air  and  with  the  vapor 
of  water,  and  involved  the  use  of  high  pressures,  up  to  1,000 
pounds  per  square  inch.  Bourne's  patents  refer  entirely 


FIG.  9. — The  Stolze  hot-air  turbine. 


THE   GAS   TURBINE. 


23 


24  THE   GAS  TURBINE. 

to  the  production  of  the  working  fluid,  and  do  not  give  any 
details  of  the  turbine  which  he  proposed  to  use. 

Another  British  patent  of  about  the  same  time  is  that 
of  James  Anderson,  this  including  the  combustion  of  a  mix- 
ture of  gas  and  air  in  the  combination  chamber  or  channel, 
the  gases  resulting  from  the  combustion  being  led  into  a 
reaction  turbine.  He  also  proposed  to  make  the  combina- 
tion chamber  in  the  arms  of  the  turbine  itself. 

It  does  not  appear  that  any  of  these  plans  were  ever  put 
into  actual  operation.  In  1872,  however,  we  find  that  Dr. 
F.  Stolze,  of  Charlottenburg,  near  Berlin,  applied  for  a 
patent  from  the  Prussian  Government  for  a  so-called  "fire 
turbine, "  this  practically  being  the  same  as  the  machine 
experimented  upon  by  Burdin  in  1847  and  described  by 
Tournaire  in  his  communication  to  the  French  Academy 
of  Sciences.  The  general  scheme  of  the  Stolze  turbine  is 
shown  in  Fig.  8,  there  being  a  multiple  turbine  compressor 
and  a  multiple  power  turbine  on  the  same  shaft,  the  com- 
pressed air  being  passed  through  a  heating  chamber  and 
thus  deriving  energy  from  the  heat  of  the  fuel  before  pass- 
ing to  the  power  turbine.  The  exterior  of  the  Stolze  turbine 
is  shown  in  Fig.  9,  this  representing  his  experimental 
machine  at  Charlottenburg. 

The  early  work  of  the  Hon.  C.  A.  Parsons  is  generally 
supposed  to  have  related  wholly  to  the  steam  turbine,  but 
in  his  original  patent  of  1884  (British  Patent  No.  6735)  the 
following  reference  to  the  gas  turbine  occurs : 

"  Motors,  according  to  my  invention,  are  applicable  to  a 
variety  of  purposes,  and  if  such  an  apparatus  be  driven,  it 
becomes  a  pump  arid  can  be  used  for  actuating  a  fluid  column 
or  producing  pressure  in  a  fluid.  Such  a  fluid  pressure- 
producer  can  be  combined  with  a  multiple  motor,  according 
to  my  invention,  to  obtain  motive  power  from  fuel  or  com- 
bustible gases  of  any  kind.  For  this  purpose  I  employ  the 
pressure-producer  to  force  air  or  combustible  gases  into  a 


THE   GAS   TURBINE. 


25 


furnace  into  which  there  may  or  may  not  be  introduced 
other  fuel  (liquid  or  solid).  From  the  furnace  the  products 
of  combustion  can  be  led  in  a  heated  state  to  the  multiple 
motor  which  they  actuate.  'Conveniently,  the  pressure-pro- 
ducer and  multiple  motor  can  be  mounted  on  the  same  shaft, 
the  former  to  be  driven  by  the  latter;  but  I  do  not  confine 
myself  to  this  arrangement  of  parts.  In  some  cases  I  employ 
water  or  other  fluid  to  cool  the  blades,  either  by  conduction 
of  heat  through  their  roots  or  by  other  suitable  arrangement 
to  effect  their  protection." 


FIG.  10. — Combustion  nozzles  of  De  Laval  gas  turbine,  1893. 

In  1893  De  Laval  proposed  to  deliver  compressed  air 
into  a  combustion  chamber  into  which  a  liquid  fuel  was 
sprayed,  the  products  of  combustion  being  directed  upon 
the  blades  of  a  wheel  similar  to  that  of  the  steam  turbine 
known  by  his  name.  The  general  arrangement  is  shown 
in  Fig.  10.  The  compressed  air  enters  at  a  and  the  sprayed 
combustible  at  b,  the  combustion  taking  place  in  the  space 
B.  At  c  provision  is  made  for  an  injection  of  water  if  neces- 
sary, the  gaseous  products  passing  through  the  nozzle  C  to 
the  wheel  D. 


26 THE   GAS   TURBINE. 

The  first  patent  of  M.  Charles  Lemale  was  taken  out  in 
1901,  followed  in  1903  by  a  more  complete  development  of 
the  combustion  chamber  and  expansion  nozzle.  M.  Lemale, 
in  conjunction  with  the  late  M.  Rene  Armengaud,  continued 
to  experiment  with  the  gas  turbine,  under  the  auspices  of 
the  Societe  des  Turbomoteurs,  and  the  results  of  this  work 
will  be  given  hereafter  at  length. 

In  the  United  States  Dr.  Sanford  A.  Moss  published,  in 
1903,  a  discussion  of  the  subject  of  the  gas  turbine,  in  the 
form  of  a  thesis  presented  to  the  faculty  of  Cornell  Univer- 
sity, this  containing  an  examination  of  the  thermodynamics 
of  the  gas  turbine  and  a  brief  account  of  some  experimental 
work. 

The  question  has  been  discussed  from  a  theoretical  view- 
point by  Mr.  R.  M.  Neilson  in  a  paper  presented  before  the 
Institution  of  Mechanical  Engineers  in  October,  1904,  which 
with  the  discussion  it  evoked  will  be  given  in  a  following 
chapter. 

It  was  also  very  fully  examined  by  members  of  the  Societe 
des  Ingenieurs  Civils  de  France  in  consequence  of  an  important 
paper  by  M.  L.  Sekutowicz,  presented  at  the  session  of  Feb- 
ruary 2,  1906,  the  discussion  being  taken  up  by  MM.  J. 
Deschamps,  Rene  Armengaud,  Jean  Rey,  G.  Hart,  L. 
Letombe,  and  A.  Bochet.  M.  Armengaud  presented  an 
important  paper  upon  the  subject  before  the  Mechanical 
Section  of  the  International  Engineering  Congress  at  Liege 
in  June,  1905,  this  having  been  revised  for  publication  in 
Cassier's  Magazine  for  January,  1907. 

In  the  Schweizerische  Bauzeitung  for  August  27,  1904 
there  appeared  an  analysis  of  the  action  of  the  Armengaud 
and  Lemale  gas  turbine  by  Alfred  Barbezat,  while  two  papers 
by  Dr.  Charles  E.  Lucke  in  the  Engineering  Magazine  of 
April,  1905,  and  August,  1906,  and  one  by  Professor  Sidney 
A.  Reeve  in  the  same  magazine  for  June,  1905,  formed  cur- 
rent contributions  to  the  theory  of  the  subject. 


THE   GAS   TURBINE.  27 

An  elaborate  investigation  of  the  practicability  of  the 
gas  turbine  was  published  in  the  Zeitschrift  fur  das  Gesamte 
Turbinenwesen  by  A.  Baumann,  of  Zwickau,  this  appearing 
in  the  issues  between  December  15,  1905,  and  May  20,  1906. 
Several  pamphlets  upon  the  subject  have  appeared  in  Ger- 
many, among  which  may  be  mentioned :  Studien  zur  Frage 
der  Gas-Turbine  (Studies  upon  the  Question  of  the  Gas  Tur- 
bine), by  Rudolf  Barkow;  Ein  Praktisch  Brauchbare  Gas- 
Turbine  (A  Practical,  Useful  Gas  Turbine),  by  Dr.  Richard 
Wegener;  and  Die  Aussischten  der  Gas  Turbine  (The  Out- 
look for  the  Gas  Turbine),  by  Felix  Langen. 

The  most  important  work  from  a  theoretical  point  of 
view  is  given  in  the  discussions  before  the  Institution  of 
Mechanical  Engineers,  in  London,  and  the  Society  of  Civil 
Engineers  of  France,  and  these  are  given  practically  entire, 
followed  by  abstracts  of  other  papers,  and  as  much  informa- 
tion concerning  actual  machines  as  can  at  present  be  made 
public. 


CHAPTER  II. 

THE  DISCUSSION  BEFORE  THE  INSTITUTION  OF 
MECHANICAL  ENGINEERS. 

ON  October  21,  1904,  Mr.  R.  M.  Neilson,  Associate  Mem- 
ber of  the  Institution  of  Mechanical  Engineers  read  before 
the  Institution  at  its  house  in  London,  a  paper  entitled: 
"A  Scientific  Investigation  into  the  Possibilities  of  Gas 
Turbines."  By  the  kind  permission  of  the  Council  of  the 
Institution  this  paper  is  here  given  entire,  together  with 
the  discussion  which  it  elicited  from  the  membership,  this 
forming  one  of  the  most  important  contributions  to  the 
question  which  has  yet  appeared  in  England. 

In  examining  this  paper  and  the  discussion  upon  it,  it 
must  be  remembered  that  at  the  time  of  its  presentation, 
1904,  the  investigations  of  Dr.  Charles  E.  Lucke  upon  tem- 
peratures and  pressures  in  free  expansion  of  hot  gases  in 
nozzles  had  not  yet  been  made  public,  nor  had  the  work  of 
Professor  Rateau  in  the  construction  of  turbine  air  com- 
pressors of  high  efficiency  been  completed. 


A  SCIENTIFIC  INVESTIGATION   INTO  THE  POSSI- 
BILITIES OF  GAS  TURBINES 

BY  MR.  R.  M.  NEILSON 

Associate  Member,  Institution  of  Mechanical  Engineers. 

A  prophecy  expressed  frequently  in  engineering  circles  at 
the  present  day  is  that  turbines  actuated  by  hot  gases  other 
than  steam  will  eventually  come  to  the  front  as  prime  mov- 
ers. The  idea  of  employing  hot  gases  (other  than  steam) 
to  drive  turbines  is  by  no  means  new;  but  the  success  of  the 
steam  turbine  has  recently  brought  the  question  into  prom- 

28 


_  THE   GAS   TURBINE.  _  29 

inence.  Although  the  subject  is  interesting  and  important, 
and  although  many  minds  seem  to  be  considering  it,  there 
appears  to  be  hardly  any  literature  on  the  subject,  except 
that  which  is  found  in  patent  records. 

There  is  no  doubt  that  many  persons  speak  of  the  advan- 
tages of  gas  turbines  without  duly  considering  the  difficul- 
ties to  be  encountered.  There  are  probably  many  others 
who  have  valuable  ideas  on  the  subject,  supported  in  some 
cases  by  experimental  data,  but  who  are  apt  to  let  their 
thoughts  run  in  a  groove  and  to  consider  (rightly  or 
wrongly)  that  the  only  possible  solution  of  the  gas  turbine 
problem  lies  in  the  particular  direction  in  which  they  are 
working. 

This  Paper  is  written  with  the  object  of  expressing  and 
and  comparing  as  concisely  as  possible  the  advantages  and 
possibilities  of  gas  turbines  worked  on  different  cycles,  and 
the  difficulties  to  be  overcome  to  make  these  turbines  a  suc- 
cess. A  further  and  more  important  object  is  to  draw  opin- 
ions from  other  engineers  who  have  studied  the  question, 
and  especially  from  those  who  have  conducted  experiments. 
If  these  objects  be  obtained,  even  in  an  imperfect  manner, 
the  author  believes  that  a  foundation  of  knowledge  will 
be  obtained  and  placed  on  record,  which  will  be  of  consider- 
able use  to  engineers  who  may  be  endeavoring  or  about  to 
endeavor  to  produce  practical  machines. 

Carnot's  formula  for  the  efficiency  of  an  ideal  heat  engine 


is  well  known,  but  its  real  meaning  is  sometimes  forgotten; 
and  it  may  not  be  out  of  place  here  to  put  in  a  reminder 
that,  in  Carnot's  cycle,  all  the  heat  is  put  in  at  tempera- 
ture T1  and  all  the  heat  withdrawn  at  temperature  T2.  An 
increase  in  the  range  of  temperature  does  not  necessarily 
cause  a  thermodynamic  gain,  and  it  is  possible  largely  to 


30  THE   GAS   TURBINE. 

increase  the  range  of  temperature  (as  for  example  by  super- 
heating steam  before  use  in  a  steam  engine)  without  ther- 
modynamically  increasing  the  efficiency  by  more  than  a, 
small  percentage. 

The  greatest  possible  efficiency  of  a  gas  engine  (recipro- 
cating or  turbine)  working  on  Carnot's  cycle  between  the 
limits  of  temperature  1600°  C.  (2912°  F.)  and  17°  C.,  will  be 
found  to  be:— 

(1600 +  273)- (17  +  273)     nQ 
1600  +  273 

If  the  gas  engine  be  an  explosion  motor  with  compression 
to  60  pounds  per  square  inch  above  atmosphere,  combustion 
at  constant  volume,  and  expansion  to  atmospheric  pressure, 
the  greatest  possible  efficiency  between  the  same  limits  of 
temperature  is  only  0.50;  and,  in  the  engine  work  on  the 
ordinary  Otto  cycle  with  the  same  compression  and  between 
the  same  limits  of  temperature,  the  greatest  possible  efficiency 
is  only  0.37. 

Efforts  must  therefore  be  made  not  so  much  to  get  the 
maximum  and  minimum  temperatures  respectively  as  high 
and  as  low  as  possible,  but  to  get  the  mean  temperature  at 
which  heat  is  given  to  the  gas  and  the  mean  temperature  at 
which  heat  is  withdrawn  from  it  respectively  as  high  and  as 
low  as  possible.  Of  these  two  temperatures  the  lower  one 
is  usually  by  far  the  more  important.  An  ideal  gas  engine 
working  on  Carnot's  cycle  between  the  limits  of  temperature 
2000°  C.  (3632°  F.)  absolute  and  300°  C.  (572°  F.)  absolute 
will  lose  as  much  by  an  increase  of  100°  C.  to  the  lower 
temperature  as  it  will  by  a  decrease  of  500°  C.  from  the 
higher  temperature. 

Coming  now  to  discuss  more  particularly  gas  turbines, 
there  are  four  cycles  on  which  it  seems  to  the  author  that 
these  could  be  worked  with  the  possibility  of  good  results. 
Two  of  these  are  what  Mr.  Dugald  Clerk  designates  Type  2 


THE   GAS   TURBINE. 


31 


and    Type    3.*     The    author    will    call    them    respectively 
Cycle  I  and  Cycle  II. 

It  has  not  been  considered  worth  while  to  discuss  the  Car- 
not  cycle  at  length,  but  a  few  remarks  are  made  about  it 
towards  the  end  of  the  Paper  (page  74). 

Y B,  B  B2  r 


O  A 

FIG.  11. — Pressure-volume  diagram. 


A  pressure-volume  diagram  of  an  engine  working  on 
Cycle  I  is  shown  in  Fig.  11,  and  an  entropy-temperature 
diagram  in  Fig.  12. 


V--- 


b;         a  /id 

FIG.  12. — Entropy-temperature  diagram. 

The  working  fluid  is  compressed  adiabatically  from  A  to 
B.  Heat  is  then  supplied  by  combustion  at  constant  pres- 
sure from  B  to  C;  the  gas  expands  adiabatically  from  C  to  D, 
and  the  fluid  is  then  cooled  at  constant  pressure  from  D  to 
A.  Reciprocating  gas  engines  have  been  worked  on  this 
cycle  by  Brayton  and  others,  but  have  never  come  into  com- 
mon use.  (The  Diesel  engine  may  be  considered  to  belong 

*  "The  Gas  and  Oil  Engine,"  by  Dugald  Clerk  (Longmans  &  Co.),  Chap- 
ter III. 


32  THE   GAS   TURBINE. 

to  this  class,  although  no  decided  constant-pressure  line  is 
discernible  on  indicator  diagrams  taken  from  the  engine.) 
One  great  difficulty  that  has  been  experienced  in  working 
reciprocating  engines  on  this  cycle  is  that  of  getting  com- 
plete combustion  during  the  period  B  C  without  the  charge 
occasionally  firing  back.  If  the  air  and  fuel  are  brought  into 
contact  only  on  entering  the  cylinder,  it  is  difficult  to  get  good 
combustion  during  the  period  B  C.  If,  on  the  other  hand,  the 
air  and  fuel  are  previously  mixed  together,  it  is  difficult 
to  prevent  occasional  firing  back.  Of  course  the  chamber 
in  which  the  air  and  fuel  are  mixed  may  be  made  strong 
enough  to  stand  explosions;  but  any  back  firing  upsets  the 
regular  working  of  the  engine  and  is  otherwise  objection- 
able. 

It  has  been  proposed  for  gas  turbines  to  cause  air  and  fuel 
to  unite  in  a  nozzle,  which  thereafter  diverges,  the  idea 
being  that  the  air  and  fuel  will  combine  on  meeting  each 
other,  and  the  hot  products  of  combustion  will  then  acquire 
a  high  velocity  in  the  divergent  nozzle  with  which  velocity 
they  will  enter  the  turbine  buckets.  The  results  of  a  trial 
of  such  a  scheme  would  be  interesting.  The  author  doubts 
if  the  combustion  would  be  quick  enough  to  give  a  good 
efficiency.  If,  however  a  combustion  chamber  of  ample 
size  were  provided  in  which  the  burning  gases  could  rest  a 
short  interval  before  passing  to  the  turbine,  better  results 
could,  in  the  author's  opinion,  be  expected.  The  air  and 
fuel  would  be  separately  pumped  into  the  chamber  from 
which  the  products  of  combustion  would  flow  continuously 
and  uniformly  by  one  or  more  passages  into  the  turbine. 

At  any  rate  the  difficulties  should  not  be  as  great  with 
turbines  working  on  this  cycle  as  with  reciprocating  engines, 
as  the  latter  have  to  receive  the  hot  gases  intermittently, 
while  the  turbine  receives  a  continuous  flow.  This  is  an 
important  point  as  regards  controlling  the  flame.  With  an 
engine  of  the  Brayton  type  the  fuel  has  to  be  ignited  in  the 


THE   GAS   TURBINE.  33 

cylinder  for  every  working  stroke,  and  the  supply  of  gas  to 
the  flame  has  to  be  cut  off  for  every  working  stroke.  With 
a  turbine  the  fuel  and  air  could  be  supplied  at  a  constant 
velocity  to  the  flame  and  a  steady  flame  maintained  without 
interruptions.  This  is  important,  because,  if  a  mixture  of 
air  and  fuel  be  always  supplied  to  the  flame  with  a  velocity 
greater  than  the  velocity  or  propagation  of  the  flame,  there 
can  of  course  be  no  firing  back,  and  this  result  can  be  ob- 
tained without  the  use  of  a  wire-gauze  screen.  The  main- 
taining of  this  velocity  of  supply  to  the  flame  above  the  re- 
quired minimum  when  starting  and  stopping  the  motor, 
and  when  running  at  low  powers,  is  of  course  a  problem 
to  be  considered,  and  some  consideration  is  given  to  it  later 
on  (pages  77  and  78).  The  strength  of  the  mixture  of  air 
and  fuel  should  be  kept  constant.  The  power  of  the  tur- 
bine can  be  varied  by  other  means,  which  will  be  referred  to 
later  (pages  77  and  78).  It  must  be  noted  that  if  the  air 
and  fuel  are  compressed  adiabatically  to  a  sufficient  extent, 
which  depends  on  the  nature  of  the  fuel,  combustion  will 
occur  immediately  the  two  are  brought  into  contact  with 
each  other.  It  is  therefore  necessary  in  such  cases  to  keep 
the  air  and  fuel  apart  until  the  instant  when  combustion  is 
desired.  It  must  also  be  noted  that  with  a  turbine  there 
will  be  no  hot  waste  gases  mixed  with  the  fresh  air  and  gas  to 
be  compressed. 

This  cycle  allows  of  a  fairly  high  ideal  efficiency  being 
obtained  with  a  moderate  maximum  temperature.  Now  a 
moderate  maximum  temperature  is  of  the  utmost  impor- 
tance in  the  case  of  a  turbine  of  the  Parsons  type.  A  Par- 
sons turbine  with  steel  blades  could  probably  be  designed 
without  any  great  difficulty  to  stand  a  temperature  of  about 
700°  C.  (1292°  F.)  without  any  water  jacketing  or  cooling 
devices  of  any  sort  (except  for  the  bearings).  With  temper- 
atures above  this,  the  blades  would  need  to  be  cooled. 
This  would  necessitate  a  radical  alteration  in  design.  The 
3 


34  THE    GAS   TURBINE. 

question  of  designing  a  turbine  to  stand  high  temperatures 
will  be  considered  later  on.  It  is  only  desired  here  to  point 
out  that  great  difficulties  with  a  certain  class  of  turbine  are 
avoided  by  keeping  the  maximum  temperature  moderate. 
The  cycle  under  consideration  may  therefore  have  great 
advantages  for  turbines. 

It  had  better  be  stated  here  that  the  author  has  made 
several  assumptions  with  regard  to  the  working  fluid  or 
fluids.  These  assumptions  are  as  follows: — 

1.  That  the  specific  heats  of  gases  dealt  with  are  con- 
stant at  all  temperatures  and  pressures,  and  are  as  follows:-— 

Specific  heat  at  constant  pressure  or  Kp  =0.238. 
Specific  heat  at  constant  volume  or  Kv=0.17 

2.  That  weight    per  cubic  foot  of   gases    dealt    with  = 
0.0777  pounds  at  a  pressure  of  15  pounds  per  square  inch 
absolute  and  a  temperature  of  17°  C. 

3.  That  PF  =  a  constant  for  all  pressures  and  temper- 
atures. 

4.  That  PF  =  a  constant  for  isothermal  expansion  and 
compression  at  all  temperatures  and  pressures. 

5.  That  combustion  produces  no  change  of  volume  ex- 
cept that  due  to  change  of  temperature. 

Some  of  these  assumptions  will  probably  be  appreciably 
inaccurate  in  certain  cases ;  but  it  seemed  advisable  to  sacri- 
fice something  for  simplicity  and  uniformity.  As  regards 
the  variability  of  the  specific  heats,  it  has .  been  thought 
better  to  assume  constancy  until  more  knowledge  on  the 
subject  has  been  obtained  and  a  scale  of  change  (if  any) 
has  been  agreed  upon. 

Pressures  have  been  reckoned  in  pounds  per  square  inch, 
and  temperatures  have  generally  been  reckoned  on  the 
Centigrade  scale,  although  for  convenience  the  corresponding 
readings  on  the  Fahrenheit  scale  have  also  been  given.  The 
numbers  on  the  diagrams  representing  pressure  and  temper- 
ature are  all  representative  of  absolute  pressures  in  pounds 


THE   GAS   TURBINE. 35 

per  square  inch,  and  temperatures  on  the  absolute  Centi- 
grade scale. 

Referring  to  Fig.  12  (page  31),  the  heat  absorbed  by  the 
fluid  is  represented  in  this  figure  by  the  area  aBCd,  and  the 
heat  abstracted  or  discarded  by  the  area  aADd.  The  heat 
converted  into  work  is  represented  by  the  area  ABCDj  and 
consequently,  if  E  represents  the  ideal  efficiency  of  an  engine 
working  on  this  cycle, 

area  ABCD 


E  = 


area  aBCd 


AT  •*  u  i  *  ^        AB      DC      Vr      ^ 

Now,  as  it  can  be  proved*  that  ~a^~==~^r~==        where  pqr 

is  any  ordinate  cutting  the  lines  ad,  AD,  and  BC,  which  are 
all  constant-pressure  lines, 

v    AB     DC 
therefore  tf____.  (1) 

Let  t  represent  the  temperature  before  compression. 
Let  Zc  represent  the  temperature  at  the  end  of  compression. 
Let  T  represent  the  temperature  at  the  end  of  combustion. 
Let  Tl  represent  the  temperature  at  the  end  of  adiabatic 
expansion. 


*  Since  all  vertical  lines  represent  adiabatic  expansion,  therefore,  by  the 
laws  of  adiabatic  expansion, 

7-1 


temp,  at  AT  press,  at  A~\ 
temp.  at  B     |_  press,  at  B  J 


where  7= 

Kv 


7-1 

Similarly         temp,  at  q  _  I"  press,  at  q  "I    y 

temp,  at  r      [_  press,  at  r  J 

But  press,  at  A  =  press,  at  q,  since  AqD  is  a  constant-pressure  line;  and  press. 
at  B  =  press,  at  r,  since  BrC  is  a  constant-pressure  line, 

therefore  temp,  at  A_  temp,  at  q 

temp,  at  B     temp,  at  r 

therefore  AB  =  DC  _qr 

aB      dC       pr 


36  THE   GAS   TURBINE. 


Then,  from  equation  (1)  and  referring  to  Fig.  12, 


This  can  be  proved  quite  well  without  any  entropy- 
temperature  diagram.*  The  diagram,  however,  shows  the 
efficiency  better. 

It  is  important  to  consider  the  amount  of  negative  work 
done  and  the  ratio  of  this  to  the  total  or  gross  work.  The 
negative  work  is  the  work  of  compressing  the  gas  and  de- 
livering it  in  its  compressed  state.  It  is  true  that  with 
some  engines  there  is  no  work  of  delivery.  In  a  reciprocat- 
ing gas  engine  in  which  the  gas  is  compressed  in  the  motor 
cylinder,  the  only  negative  work  (ideally)  is  that  of  com- 
pressing the  charge;  and,  even  when  a  separate  cylinder  is 
used  for  the  compression,  the  work  of  delivering  might  be 
avoided.  With  a  turbine,  however,  the  fluid  cannot  be  com- 
pressed in  the  motor;  and,  whatever  arrangement  is  adopted, 
the  compressed  fluid  will  have  to  be  delivered  after  compres- 
sion. The  author  has,  therefore,  considered  it  better  in  all 
cases  to  include  in  the  negative  work  the  amount  required 
to  deliver  the  compressed  gas.  The  motor  proper  of  course 
gets  the  benefit  of  this  work. 

In  Fig.  11  (page  31)  the  work  to  compress  the  gas  is 
represented  by  the  area  AbB,  and  the  work  to  deliver  it  in 
compressed  state  by  the  area  yYBb.  The  total  negative 
work  is  therefore  represented  by  the  area  yYBA.  The  gross 
work  of  the  motor  is  represented  by  the  area  yYCD,  of  which 
the  part  yYBb  represents  the  work  done  before  expansion, 
and  the  part  bBCD  the  work  done  during  expansion.  By 
deducting  the  negative  work  from  the  gross  work  the  net 
work  is  obtained;  this  is  represented  by  the  area  ABCD. 
This  net  work  is  the  same  as  that  represented  on  the  en- 
tropy-temperature diagram,  Fig.  12  (page  31),  by  the  area 
ABCD. 

*  See  "The  Gas  and  Oil  Engine,"  by  Dugald  Clerk,  pages  46-48. 


THE   GAS   TURBINE.  37 

Cycle  I,  Case  1. 

If  the  gas  is  required  to  be  used  in  a  Parsons  turbine  with- 
out cooling  arrangements  the  maximum  temperature  must 
not  exceed  700°  C.  (1292°  F.).  A  case  with  this  maximum 
temperature  will  now  be  considered : — 

In  all  cases — 

Let  t  and  p  represent  respectively  absolute  temperature  C.  and  absolute  pres- 
sure pounds  per  square  inch  before  compression. 

Let  tc  and  p0  represent  respectively  absolute  temperature  C.  and  absolute  pres- 
sure pounds  per  square  inch  after  compression. 

Let  T  and  P  represent  respectively  absolute  temperature  C.  and  absolute  pres- 
sure pounds  per  square  inch  after  combustion. 

Let  Tl  and  P,  represent  respectively  absolute  temperature  C.  and  absolute 
pressure  pounds  per  square  inch  after  expansion  to  atmospheric  pressure. 

Let  v  represent  one  cubic  foot  of  the  fluid  at  temperature  t  and  pressure  p. 

Let  vc,  V  and  V,  represent  the  volume  of  the  same  at  tc,  pc',  T,  P,  and  Tlt 
P1  respectively. 

Suppose  that  in  all  cases  t  =  17°  C.  (290°  absolute  C.)  and 
the  corresponding  pressure  =  15  pounds  absolute.  First 
by  compressing  to  42  pounds  absolute:  tc  will  then  be  389° 
absolute  C.  This  compression  is  shown  by  the  line  AB  on 
the  pressure-volume  diagram,  Fig.  13  (page  38),  and  on  the 
entropy-temperature  diagram,  Fig.  14. 

Let  heat  be  supplied  and  the  gas  expand  at  constant  pres- 
sure along  the  line  BC  till  the  temperature  is  973°  absolute 
C.  Let  the  gas  expand  adiabatically  along  the  line  CD  till 
the  pressure  falls  to  15  pounds  absolute.  The  fluid  is  then 
exhausted  into  atmosphere,  and  as  the  new  charge  is  taken 
at  the  same  pressure  and  at  temperature  t,  it  can  be  assumed 
that  the  discharged  gas  is  cooled  at  constant  pressure  and 
used  over  again.  Both  diagrams  can  therefore  be  com- 
pleted by  the  constant-pressure  line  DA. 

The  heat  absorbed  by  the  fluid  is  represented  by  the  area 
aBCd  in  Fig.  14,  and  the  heat  rejected  by  the  area  aADd. 
The  heat  converted  into  work  is  represented  by  the  area 
ABCD  and 

area  ABCD  ^c- *  =  389  -  290  =  99 
~     tc  389       ~389 


38 


THE   GAS   TURBINE. 


The  negative  work  is  represented  in  Fig.  13  by  the  area 
yYBA,  the  gross  work  by  the  area  yYCD,  and  the  net  work 
by  the  area  ABCD,— 

negative  work  _  area  yYBA 
gross  work         area  yYCD 


therefore         — — — 


0.4. 


f  • 

\  2  3 

Volume 

FIG.  13. — Cycle  I,  Case  1.     Pressure-volume  diagram. 

The  expansion  line  is  carried  right  down  to  atmosphere. 
It  should  be  possible  in  practice  without  difficulty  to  do  this 
very  nearly  in  a  turbine,  although  the  volume  at  D  is  2} 
times  the  volume  at  A.  In  dealing  with  large  volumes  and 

C  T-973 


T-725 


\\\\\\\\\\\\\\\\\\\\\\\ 


FIG.  14. — Cycle  I,  Case  1.    Entropy-temperature  diagram. 

small  pressures  there  is  an  immense  difference  between  tur- 
bines and  reciprocating  engines.  Reciprocating  engines  re- 
quire large  cylinders.  These  large  cylinders,  besides  being 
objectionable  on  account  of  bulk  and  cost,  necessitate  great 
frictional  losses.  The  low  pressure  dealt  with  is  of  little 
import  as  regards  friction,  which  will  be  nearly  the  same 
whether  the  pressure  is  13  pounds  below  atmosphere  or 
13  pounds  above  atmosphere.  With  a  turbine,  however. 


THE   GAS   TURBINE.  39 

the  large  volume  of  the  fluid  does  not  necessitate  such  a 
bulky  machine.  Moreover  in  a  turbine  the  friction  depends 
on  the  pressure.  With  high  pressures  the  friction  is  great, 
with  low  pressures  very  small.  (In  marine  propulsion  by 
steam  turbines  it  is  not  considered  worth  while  uncoupling 
the  reversing  turbines  when  the  vessel  is  going  ahead. 
These  turbines  are  allowed  to  rotate  (above  their  normal 
speed)  in  the  low  pressure  which  exists  at  the  exhaust  ends 
of  the  main  low-pressure  turbines. 

Cycle  I,  Case  2. 

700°  C.  (1292°  F.)  must  not,  however,  be  considered  as 
the  limiting  temperature  for  gas  turbines.  Much  higher 
temperature  can  be  employed  if  water-cooling  or  other 
cooling  arrangements  be  used.  Mr.  Parsons  has  circulated 
steam  for  heating  purposes  through  passages  formed  in  the 
rings  supporting  the  fixed  blades  of  his  radial-flow  steam 
turbines.*  Water  could  as  easily  be  circulated,  and  there 
should  be  no  great  difficulty  in  passing  the  water  also  through 
the  rings  supporting  the  moving  blades. 

It  has  been  proposed  by  Mr.  Parsons  and  others  to  circu- 
late water  or  other  cooling  fluid  through  the  actual  blades 
of  a  turbine,  these  being  formed  hollow.  It  has  also  been 
proposed  to  keep  the  blades  of  a  single-wheel  turbine  cool 
by  causing  the  actuating  fluid  to  act  only  at  one  point  of  the 
circumference  of  the  wheel,  while  a  cooling  fluid  is  projected 
onto  the  blades  at  another  point. 

By  the  employment  of  cooling  devices  a  turbine  might 
possibly  be  made  to  stand  a  temperature  of  1500°  C. 
(2732°  F.)  or  even  2000°  C.  (3632°  F.).  2000°  C.  is  a  very 
high  temperature,  and  there  would  be  great  difficulty  in  de- 
vising and  constructing  cooling  arrangements  which  would 
keep  the  blades  in  good  working  order  when  acted  on 

*  "  The  Steam  Turbine,"  by  R.  M.  Neilson  (Longmans  and  Co.) ,  pp.  43-45. 


40  THE   GAS   TURBINE. 

by  gas  at  a  temperature  approaching  this.  Let  it  be  as- 
sumed, however,  that  2000°  C.  is  allowable  for  the  maximum 
temperature;  then,  if  the  same  compression  is  kept  as  in 
Case  1,  the  ideal  pressure- volume  and  entropy-temperature 
diagrams  will  be  as  shown  in  Figs.  15  and  16.  In  these 
Figs,  the  line  CD  has  been  reproduced  from  Figs.  13  and  14 
(page  38),  and  is  shown  in  dotted  lines  in  order  that  the 
two  cases  may  be  readily  compared. 


•5-845 
5  V 


FIG.  15.  —  Cycle  I,  Case  2.     Pressure-volume  diagram. 

Referring  to  Fig.  16  the  heat  absorbed  by  the  fluid  is  rep- 
resented by  the  area  aBEf,  the  heat  rejected  by  the  area 
aAFf,  and  the  heat  converted  into  work  by  the  area  ABEF. 


Therefore  P1     ~~~       tc    * 


area  aBEj 

389-290 
389 


0.25. 


The  increase  in  the  maximum  temperature  has,  therefore, 
added  nothing  to  the  efficiency,  and  this  will  always  be  the 
case  if  the  initial  temperature  and  pressure  are  unchanged 
and  compression  is  made  to  the  same  amount.  That  is  to 
say,  as  long  as  the  constant  pressure  lines  are  started  from 
the  same  points,  A  and  B,  they  can  be  extended  any  dis- 
tance to  the  right  and  connected  by  any  adiabatic  line; 
E  will  remain  unchanged.  In  Fig.  16  the  additional  area 
dCEf  is  divided  by  the  line  DF  in  the  same  ratio  as  the  orig- 
inal area  aBCd  is  divided  by  the  line  AD. 

The  negative  work  (in  Case  2)  is  represented  in  Fig.  15 
by  the  area  yYBA',  it  is  the  same  as  in  the  last  case.  The 


THE   GAS  TURBINE. 


41 


gross  work  is  represented  by  the  area  yYEF,  and  the  net 
work  by  the  area  ABEF, 


Therefore 


negative  work     area  yYBA 


^  =  0.171. 


gross  work        area  yYEF 
The  ratio  of  negative  work  to  gross  work  has,  therefore, 


been  very  considerably  diminished. 


E  T-2273 


TH695 


a 


FIG.  16. — Cycle  I,  Case  2.    Entropy-temperature  diagram. 

Cycle  I,  Case  3. 

In  Case  1  it  was  necessary  to  have  a  low  compression  be- 
cause a  high  compression  with  a  maximum  temperature  of 
only  700°  C.  (1292°  F.)  would  have  given  an  impractically 
high  value  to  the  ratio  of  negative  work  to  gross  work.  In 


42 


THE   GAS  TURBINE. 


fact  this  ratio    was  high  even  with  the  low  compression 
adopted. 

With  the  maximum  temperature  raised  to  2000°  C. 
(3632°  F.),  however,  a  much  higher  compression  can  be 
adopted.  Suppose  a  compression  to  300  pounds  per  square 
inch  absolute  is  adopted.  This  will  make  tc  682.5°  absolute 
C.  (1260.5°  F.).  The  pressure-volume  and  entropy-tem- 
perature diagrams  will  then  be  as  shown  in  Figs.  17  and  18. 


FIG.  17. — Cycle  I,  Case  3.     Pressuie-volume  diagram. 


Referring  to  Fig.  18  it  is  seen  that 

area  AGHK 


E 


area  aGHk 
L-t     682.5-290 


682.5 


=  0.58 


which  is  much  better  than  (more  than  double)  that  in  Cases 
1  and  2.  There  is,  however,  the  inconvenience  of  a  high  com- 
pression, and  compared  with  Case  1  more  heat  is  likely  to  be 
lost  through  radiation  owing  to  the  higher  average  temper- 
ature. This  question  of  radiation  will  be  more  or  less  impor- 
tant according  to  the  type  of  turbine. 

The  negative  work  is  represented  in  Fig.  17  by  the  area 


THE   GAS  TURBINE. 


43 


zZGA,  the  gross  work  by  the  area  zZHK,  and  the  net  work 
by  the  area  AGHK. 

—,,        .  negative  work      area  zZGA        0 

Therefore  —. —  = ,7w — =0.3. 

gross  work 


•2213 


£•=6825 


FIG.  18. — Cycle  I,  Case  3.    Entropy-temperature  diagram. 

Cycle  I,  Case  4. 

It  will  be  interesting  to  find  what  efficiency  can  be  ob- 
tained with  a  maximum  temperature  of  2000°  C.  (3632°  F.) 
by  increasing  the  compression  till  the  ratio  of  negative  work 
to  gross  work  is  0.4 — the  same  as  in  Case  1.  This  ratio  will 
be  attained  when  tc  =  909°  absolute  C.  (1668°  F.),  which 
corresponds  to  a  pressure  of  818  pounds  absolute. 


Then 


„ 

E=       909 


44 


THE   GAS  TURBINE. 


The  pressure-volume  and  entropy-temperature  diagrams 
for  this  case  are  given  in  Figs.  19  and  20. 

The  line  BG  is  shown  dotted  on  Fig.  20  to  allow  Case  4 
to  be  compared  with  Case  1. 


Volume 
FIG.  19. — Cycle  I,  Case  4.    Pressure- volume  diagram. 

The  sharp  corner  at  M  would  likely  be  rounded  off  in 
practice.  This  would  reduce  the  efficiency  slightly.  It 
would  also,  however,  reduce  the  maximum  temperature,  and 
for  this  reason  it  might  be  advantageous  in  some  cases  to 
round  off  the  corner  intentionally. 


THE   GAS   TURBINE. 


45 


In  every  case  it  has  been  assumed  that  the  compression  is 
adiabatic;  it  is  usually  important  that  it  should  be  at  least 
nearly  so.  If,  for  example,  in  Figs.  11  and  12  (page  31) 
the  compression,  instead  of  being  along  the  adiabatic  AB 
had  been  along  the  line  ABl}  which  is  below  the  adiabatic 
line,  that  is,  if  heat  had  been  allowed  to  escape  during  the 


MT*2273 


fc-909 


T.-725 


a 


FIG.  20. — Cycle  I,  Case  4.    Entropy-temperature  diagram. 

compression,  the  heat  absorbed  by  the  fluid  for  the  same 
value  of  T  would  have  been  increased  by  the  area  b^B^Ba  in 
Fig.  12,  while  the  heat  converted  into  work  would  have 
been  increased  only  by  the  relatively  small  area  AB^B. 
E  would,  therefore,  have  been  reduced. 

If  on  the  other  hand  the  compression  had  been  along  the 
line  AB2,  which  is  above  the  adiabatic,  that  is,  if  heat  had 


46  THE   GAS   TURBINE. 

been  put  into  the  fluid  during  compression,  the  heat  ab- 
sorbed and  the  heat  converted  into  work  would  both  have 
been  reduced  by  the  same  amount,  namely,  the  area  ABB2. 
E  would,  therefore,  obviously  be  reduced  in  this  case  also, 
assuming  that  the  heat  put  into  the  fluid  during  compression 
is  obtained  by  the  combustion  of  fuel. 

If,  however,  the  heat  put  into  the  fluid  during  compression 
is  obtained  for  nothing — if,  for  example,  it  is  heat  that  would 
otherwise  be  radiated  away  or  carried  away  by  convexion— 
the  effect  on  E  is  not  obvious. 

A  compression  along  the  line  AB2,  Figs.  11  and  12,  will 
give  a  higher  value  to  E  than  a  compression  along  the  line 
AB,  if  the  heat  absorbed  during  the  compression  AB2  is  got 
for  nothing,  and  if  the  two  cases  are  otherwise  the  same; 
but  a  compression  along  the  line  AB2  produces  a  higher  ratio 
of  negative  work  to  gross  work.  This  will  be  clear  from  Fig. 
11.  Now  with  this  ratio  of  negative  work  to  gross  work, 
a  still  higher  efficiency  could  be  obtained  by  keeping  the  com- 
pression adiabatic  and  continuing  it  further.  A  hot  com- 
pression, such  as  along  the  line  AB2J  when  the  heat  is  got  for 
nothing,  may  be  advantageous  in  a  few  cases,  viz.,  T1  is  low 
compared  with  tc]  but  generally  such  a  compression  will  be 
harmful. 

It  is,  in  general,  disadvantageous  to  heat  the  air  or  fuel 
before  compression,  no  matter  what  be  the  source  of  heat. 

If  gas  is  allowed  to  enter  a  water-cooled  turbine  at  a  high 
temperature,  such  as  2000°  C.  (3632°  F.),  there  will  neces- 
sarily be  a  great  amount  of  heat  carried  away  by  the  water. 
In  a  reciprocating  engine  the  metal  surface  with  which  the 
gas  comes  into  contact  is  very  small  compared  with  that  in  a 
multiple-expansion  turbine;  and  in  a  reciprocating  engine 
the  bulk  of  the  gas  may  expand  and  fall  from  its  maximum 
temperature  to  the  temperature  at  exhaust  without  ever 
coming  near  a  metal  surface.  In  a  multiple-expansion  tur- 
bine, on  the  other  hand,  every  particle  of  gas  must  practi- 


THE   GAS   TURBINE.  47 

cally  slide  along  a  metal  surface  immediately  it  comes  to  the 
first  ring  of  blades.  With  turbines  employing  gas  which 
enters  the  turbine  casing  at  such  a  temperature,  the  heat 
lost  through  the  walls  and  carried  away  by  the  water  must 
necessarily  be  very  great  indeed.  It  is  true  that  the  metal 
surface  in  contact  with  the  gas  can  be  allowed  to  be  at  a 
much  higher  temperature  than  the  inside  of  the  cylinder 
walls  of  a  reciprocating  engine;  but,  in  spite  of  this,  the 
heat  lost  through  the  walls  and  carried  away  by  the  cooling 
water  (or  other  cooling  medium)  will  probably  be  much 
greater  with  a  turbine  actuated  by  gas  entering  the  turbine 
casing  at  about  2000°  C.  than  in  a  reciprocating  engine  in 
which  the  maximum  temperature  is  2000°  C.  This  loss  of 
heat  will  cause  the  actual  work  done  by  the  engine  to  be  very 
much  below  the  ideal.  This  is  not  only  important  in  itself, 
but,  as  will  be  explained  subsequently  (pages  50  and  51), 
it  prevents  useful  employment  of  a  high  ratio  of  negative 
work  to  gross  work.  The  question  of  utilizing  this  lost  heat 
will  be  discussed  later  on  pages  59  to  66. 

Cycle  I,  Case  3a. 

Instead  of  employing  cooling  arrangements  for  the  metal, 
some  or  all  of  the  available  heat  energy  of  the  gas  can  be 
converted  into  kinetic  energy  before  causing  it  to  act  on  the 
turbine,  so  that  the  latter  is  not  exposed  to  an  unduly  high 
temperature.  This  can  be  done  by  allowing  the  gas,  when 
at  the  maximum  temperature,  to  expand  in  a  divergent 
nozzle  till  its  temperature  falls  to  a  degree  that  the  turbine 
can  stand.  More  than  one  nozzle  can  be  employed,  but,  to 
reduce  the  radiation  losses,  the  nozzles  should  be  large  and 
few  in  number. 

Suppose  that  the  gas  is  compressed  adiabatically  to  300 
pounds  absolute,  and  then  is  heated  at  constant  pressure  to 
a  temperature  of  2273°  absolute  C.  (4132°  F.),  as  in  Case  3. 
If  now  the  gas  be  allowed  to  expand  in  a  suitable  nozzle, 


48  THE   GAS   TURBINE. 

adiabatic  expansion  can  be  obtained;  and  if  this  be  continued 
till  the  pressure  falls  to  15  pounds  absolute  the  temperature 
will  be  966  absolute  C.  (693°  C.).  This  is  just  below  the 
temperature  which  was  fixed  on  as  a  maximum  for  a  turbine 
without  artificial  cooling.  The  entropy-temperature  diagram 
will  be  the  same  as  in  Case  3,  Fig.  18  (page  43) ,  and  E 
will  therefore  be  the  same,  namely  0.58.  The  ratio  of  nega- 
tive work  to  gross  work  will  also  be  the  same  as  in  Case  3, 
namely  0.3. 

Referring  to  the  pressure-volume  diagram  for  Cycle  I 
Case  3,  Fig.  17  (page  42),  the  area  zZHK  represents  the 
kinetic  energy  of  the  gas  leaving  the  nozzle,  which  kinetic 
energy  equals  33,840  foot-pounds.  This  is  for  a  quantity 
of  gas  which  measures  1  cubic  foot  at  A.  The  velocity  is 
5290  feet  per  second. 

For  the  sake  of  comparison  it  may  be  advantageous  to 
mention  the  velocities  of  the  steam  jets  employed  in  De 
Laval  steam  turbines.  If  saturated  steam  at  50  pounds, 
absolute  pressure  is  expanded  adiabatically  to  a  pressure  of 
0.6  pounds  absolute,  which  corresponds  to  a  temperature 
of  85°  F.,  and  its  heat  energy  turned  into  kinetic  energy, 
the  velocity  acquired  works  out  at  3690  feet  per  second. 
If  saturated  steam  at  300  pounds  absolute  pressure  were 
treated  similarly,  the  velocity  would  be  4380  feet  per 
second.  The  velocities  actually  obtained  in  practice  must 
be  somewhat  less  than  these  figures,  owing  to  friction  in 
the  nozzles. 

To  get  the  best  results  from  a  fluid  velocity  such  as  5290 
feet  per  second  would  require,  with  a  single  turbine  wheel,  a 
vane  speed  which  cannot  be  obtained  at  present  for  want  of 
a  sufficiently  strong  and  light  material — the  stresses  pro- 
duced by  centrifugal  force  are  too  great.  This  difficulty  is 
experienced  with  De  Laval  turbines.  The  obvious  way  out 
of  the  difficulty  is  to  employ  several  wheels  in  series,  the  gas 
passing  through  the  several  wheels  with  diminishing  velocity, 


THE   GAS   TURBINE.  49 

but  with  nearly  constant  pressure.  This  has  been  done  in 
steam  turbines. 

With  the  same  object  of  reducing  the  vane  speed,  a  device 
has  been  proposed  whereby  the  nozzles  are  mounted  on  a 
wheel  which  rotates  in  the  opposite  direction  to  the  wheel 
carrying  the  vanes.  If  the  two  wheels  rotate  at  the  same 
speed  (in  opposite  directions)  this  speed  will  be  half  of  that 
of  the  single  wheel  if  the  nozzles  were  stationary.  The  cen- 
trifugal force  is,  therefore,  only  one-fourth  of  what  it  would 
otherwise  be. 

The  frictional  losses  in  the  nozzles  of  a  gas  turbine  will 
probably  be  less  than  those  in  the  nozzles  of  a  steam  turbine 
for  the  same  velocity  of  exit  from  the  nozzle. 

Cycle  I,  Case  4a. 

If  one  tries  to  work  to  the  same  entropy-temperature 
diagram  as  in  Case  4,  Fig.  20  (page  45),  but  employs  a 
divergent  nozzle,  as  in  Case  3a,  to  reduce  the  maximum 
temperature  to  700°  C.,  so  that  the  gas  can  be  used  in  a  tur- 
bine without  cooling  arrangements,  Tl  in  this  case  will  be 
725°  absolute  C.  (452°  C.).  It  is  not  necessary,  therefore,  to 
perform  all  the  adiabatic  expansion  in  a  divergent  nozzle,  but 
a  portion  of  it  can  be  performed  in  the  turbine.  If  the  fluid 
is  expanded  in  the  nozzle  only  till  its  temperature  falls  to 
700°  C.  (1292°  F.),  the  pressure  will  then  be  42  pounds  abso- 
lute; so  that  27  pounds  can  be  dropped  in  the  turbine. 

Referring  to  the  pressure-volume  diagram  for  Cycle  I, 
Case  4,  Fig.  19  (page  44),  the  line  qQ  is  drawn  to  represent 
the  pressure  at  which  the  gas  leaves  the  nozzle.  The  kinetic 
energy  of  the  gas  leaving  the  nozzle  is  represented  by  the 
area  XMQq.  It  can  be  ascertained  that  this  amounts  to 
33,660  foot-pounds  (for  one  cubic  foot  of  gas  measured  at  A), 
and  the  velocity  works  out  at  5280  feet  per  second.  E  will 
be  the  same  as  in  Case  4,  and  so  will  the  ratio  of  negative 
work  to  gross  work. 


50 THE   GAS   TURBINE. 

It  seems  to  the  author  that  an  engine  working  on  this 
cycle,  according  to  Case  3a  or  Case  4a,  or  between  these,  has 
good  prospects.  The  ideal  efficiency  is  high — from  0.58  to 
0.68.  How  near  one  could  approach  this  efficiency  in  prac- 
tice would  depend,  of  course,  both  on  the  losses  in  the  motor 
proper  and  on  the  losses  in  the  pump. 

The  losses  in  the  motor  proper  may  be  taken  to  include 
the  losses  in  the  combustion  chamber,  if  such  is  employed, 
and  in  the  nozzles.  The  motor  losses  will  then  consist  of  :— 

1.  Loss  of  heat  by  radiation  and  conduction. 

2.  Fluid  friction. 

3.  Friction  in  turbine  bearings. 

4.  Loss  due  to  incomplete  expansion. 

The  first  loss  will  be  large,  but  should  be  less  than  in  re- 
ciprocating engines,  owing  to  the  higher  velocities  employed 
and  to  the  higher  temperatures  allowable  in  the  metal. 

The  second  loss  will  be  considerable,  but  much  less  than  in 
turbines  using  saturated  steam.  It  has  been  found  by  ex- 
periment that  hot  dry  air  causes  much  less  friction  than  wet 
steam.  (The  steam  is  always  wet  in  a  De  Laval  turbine 
casing,  unless  it  enters  the  nozzles  with  a  large  amount  of 
superheat.) 

The  third  loss  will  be  trifling  and  the  fourth  loss  should  be 
moderate.  The  discharge  of  heat  with  the  exhaust  gases  is 
here  only  considered  as  a  loss  in  so  far  as  it  exceeds  that  of  an 
ideal  engine. 

It  is. difficult  to  estimate  the  pump  losses.  Rotary  com- 
pressors on  the  turbine  principle  seem  to  have  been  em- 
ployed up  to  only  about  80  pounds  pressure.  Whether  or  no 
they  are  suitable  for  high  pressures  is  a  point  which  it  is  very 
desirable  to  ascertain.  One  would  be  inclined  to  believe  that 
the  fluid  frictional  losses  with  such  machines  would  be  very 
great  if  attempts  were  made  to  obtain  high  pressures.  It 
by  no  means  follows,  however,  that  a  fairly  efficient  rotary 
air  compressor  cannot  be  devised. 


THE   GAS  TURBINE.  51 

A  reciprocating  compressor  always  has  the  disadvantage 
that  the  air  when  drawn  in  becomes  heated  by  contact  with 
the  hot  metal  surfaces  before  compression  commences.  This 
evil  is  reduced  by  compounding.  It  is  an  evil  which  occurs 
to  a  serious  extent  with  reciprocating  gas  engines  working 
on  the  Otto  cycle. 

With  a  reciprocating  compressor  it  will  be  difficult  to 
avoid  the  necessity  of  jacketing  the  cylinder  if  high  compres- 
sions are  employed.  This  will  bring  the  compression  curve 
below  the  adiabatic  and  reduce  the  efficiency  as  before  ex- 
plained. 

In  any  case,  whatever  be  the  nature  of  the  pump,  there  is 
bound  to  be  a  certain  amount  of  heat  passed  through  the 
walls  of  the  pump  cylinders  or  casing.  If  this  loss  be  made 
up  by  friction  or  impact  within  the  pump,  the  compression 
may  be  along  an  adiabatic  curve,  but  the  loss  will  still  have 
to  be  considered. 

The  ratio  of  negative  work  to  gross  work  (in  the  particular 
cases  here  referred  to)  is  somewhat  high — 0.3  to  0.4.  In 
the  case  of  a  turbine  one  need  not  fear  the  increase  in  the 
bulk  of  the  engine  due  to  this  high  ratio;  for  the  bulk  of  the 
turbine  will  probably  be  very  small  for  the  power.  Fric- 
tional  and  other  losses  become,  however,  of  much  greater 
importance  when  the  ratio  is  high.  To  show  this  forcibly, 
consider  an  extreme  case.  Suppose  that  the  ratio  of  nega- 
tive work  to  gross  work  in  an  ideal  engine  is  0.5,  or,  in  sim- 
pler language,  suppose  the  pump  requires  half  the  gross 
power  of  the  machine,  there  being  no  friction.  If  now  the 
machine  is  not  ideal,  and  if  the  mechanical  efficiency  of  the 
pump  is  only  f  and  that  of  the  motor  proper  only  f ,  no  useful 
work  whatever  will  be  got  out  of  the  machine — all  the  work 
will  be  absorbed  by  friction.  For,  if  the  power  of  the  motor 
proper,  including  that  spent  on  friction,  is  100,  the  pump 
will  require  50,  and  as  its  efficiency  is  §,  it  will  take  75.  This 
is  exactly  what  the  motor  will  give  out  after  deducting 


52 


THE   GAS   TURBINE. 


friction.  There  will,  therefore,  be  no  power  got  out  of  the 
machine.  When  there  is  a  high  ratio  of  negative  work  to 
gross  work,  success  will,  therefore,  be  dependent  largely  on 
the  efficiency  of  the  pump.  Unless  the  pump  is  at  least 
fairly  efficient,  success  cannot  be  expected.  In  the  Diesel 
engine  the  bulk  of  the  air  is  compressed  to  about  500  pounds 
per  square  inch,  and  the  air  which  carries  the  oil  into  the 
cylinder  is  compressed  from  100  pounds  to  200  pounds 
higher.*  It  would  be  interesting  to  know  with  what  effi- 
ciency the  air  is  compressed  in  the  Diesel  engine. 


[53 
•0256 


Volume 

FIG.  21  — Cycle  II,  Case  1.    Pressure-volume  diagram. 


Otto  cycle  reciprocating  engines  having  ideal  efficiencies 
of  0.4  to  0.45  have  given  practical  efficiencies  of  half  that 
amount.  By  practical  efficiency  is  meant  ratio  of  brake 
horse-power  to  thermal  units  in  gas  consumed,  calculated  on 
the  higher  calorific  value.  When  the  ideal  efficiency  is 

*"The  Diesel  Engine,"  by  H.  Ade  Clark.  Proceedings,  Inst.  Mech. 
Engrs.,  1903,  Part  3,  page  395. 


THE   GAS   TURBINE. 


53 


increased  above  0.45,  the  ratio  of  practical  efficiency  to  ideal 
efficiency  usually  falls  below  0.5 — the  greater  the  ideal  effi- 
iency,  the  greater  are  the  losses.  With  a  turbine  the  losses 
ought  also  to  increase  when  the  ideal  efficiency  is  increased, 
but  whether  to  the  same  extent  as  with  an  Otto  engine  it  is 


TT=2273 


Tf855 


frsocfi 


^=290 


FIG.  22. — Cycle  II,  Case  1     Temperature-entropy  diagram. 

difficult  to  say.  When  considering  high  compressions,  it  is 
well  to  note  that  the  Diesel  engine,  with  a  high  compression 
and  an  incomplete  expansion,  has  given  some  of  the  highest 
practical  efficiencies  yet  attained.  The  compression  should 
not  cause  the  same  trouble  in  starting  a  turbine  as  in  starting 
a  reciprocating  engine,  as  with  a  turbine  it  should  be  practi- 
cable to  arrange  that  at  every  instant  the  gross  work  is 


54  THE    GAS   TURBINE. 

greater  than  the  negative  work.  With  a  reciprocating 
engine  having  a  single  cylinder  working  on  the  Otto  cycle 
there  are,  of  course,  periods  when  the  negative  work  exceeds 
the  gross  work. 

Cycle  II,  Case  1. 

With  regard  to  explosion  turbine  engines,  suppose  that 
the  fluid  is  compressed  adiabatically  to,  say,  101  pounds  per 
square  inch  absolute,  that  is  to  a  temperature  of  500°  abso- 
lute C.  (932°  F.).  Let  it  now  be  heated  at  constant  volume 
by  explosion,  and  let  there  be  a  mixture  of  such  a  strength 
that  the  temperature  will  rise  to  2000°  C.  (2273°  absolute 
C.).  The  pressure  will  then  be  459  pounds  absolute.  If  the 
gas  is  now  allowed  to  expand  adiabatically  till  its  pressure 
is  atmospheric  (when  its  temperature  will  be  855°  absolute 
C.),  and  then  cooled  at  that  pressure  till  it  resumes  its 
original  state,  the  pressure-volume  and  entropy-temperature 
diagrams  will  be  as  shown  in  Figs.  21  and  22  (pages  52  and  53). 

In  Fig.  22  the  heat  supplied  to  the  fluid  is  represented  by 
the  area  aRTs,  the  heat  rejected  by  the  area  aASs,  and  the 
heat  converted  into  work  by  the  area  ARTS. 

area  ARTS 
Therefore 


The   negative  work   can    be  compared  with   the   gross 
work  in  Fig.  21.     The  ratio  of  negative  work  to  gross  work 


area  v  VRA 

Cycle  II,  Case  1,  very  nearly  resembles  common  practice 
to-day  with  reciprocating  explosion  engines.  The  expansion 
is,  however,  continued  to  atmospheric  pressure.  This  as  a 
rule  is  not  desirable  in  a  reciprocating  engine,  on  account  of 
the  extra  length  required  to  be  given  to  the  engine  cylinder, 
which  not  only  increases  the  loss  by  friction  but  increases 


THE   GAS   TURBINE.  55 

the  loss  of  heat  by  the  expanding  gas  and,  if  the  same 
length  of  stroke  is  employed  for  drawing  in  the  fresh  charge, 
increases  the  heating  of  the  charge  before  compression. 
The  case,  however,  is  very  different  with  turbines;  and  there 
seems  no  good  reason  why  with  these  the  adiabatic  expan- 
sion should  not  be  carried  practically  to  atmospheric  pres- 
sure. 

In  practice  the  maximum  pressure  and  the  average  maxi- 
mum temperature  throughout  the  gas  would  be  less  than  the 
values  here  indicated,  owing  to  radiation  losses. 

Cycle  II,  Case  la. 

The  gas  could  not  be  allowed  into  an  uncooled  turbine  at 
the  maximum  temperature  in  Cycle  II,  Case  1;  but,  if  the 
expansion  was  performed  wholly  or  nearly  wholly  in  a 
divergent  nozzle,  the  temperature  of  exit  from  the  nozzle 
would  be  sufficiently  low  to  allow  of  the  gas  entering  an 
uncooled  turbine. 

For  example,  if  the  gas  at  the  maximum  temperature  of 
2273°  absolute  C.  (4123°  F.)  and  the  maximum  pressure 
of  459  pounds  absolute  were  expanded  in  a  perfect  divergent 
nozzle  till  the  temperature  fell  to  700°  C.  (973°  absolute 
C.),  which  was  fixed  on  as  the  maximum  allowable  temper- 
ature in  an  uncooled  turbine,  the  mean  pressure  on  leaving 
the  nozzle  would  be  23.5  pounds  absolute.  The  kinetic 
energy  of  the  gas  (1  cubic  foot  at  A)  on  leaving  the  nozzle 
would  be  represented  by  the  area  VRTQ&  in  Fig.  21,  and 
would  amount  to  20,500  foot-pounds.  The  mean  velocity 
(the  square  root  of  the  mean  square)  would  be  4120  feet  per 
second. 

On  comparing  Cases  1  and  la  of  Cycle  II  by  reference  to 
the  Table  (page  75)  with  Cases  2,  3,  3a,  4  and  4a  of  Cycle  I, 
which  have  the  same  maximum  temperature,  it  will  be  found 
that  the  efficiency  is  very  much  greater  than  Cycle  I,  Case  2; 
is  nearly  as  great  as  Cycle  I,  Cases  3  and  3a;  and  is  con- 


56  THE   GAS   TURBINE. 

siderably  below  Cycle  I,  Cases  4  and  4a.  The  ratio  of  nega- 
tive work  to  gross  work  is,  however,  greater  than  in  Cycle  I, 
Case  2,  and  less  than  in  Cases  3,  3a,  4  and  4a  of  Cycle  I. 

There  are  two  objections  to  the  use  for  turbines  of  a  cycle 
such  as  Cycle  II,  and  these  objections  must  be  set  against  the 
advantage  which  turbines  would  possess  over  reciprocating 
explosion  motors,  in  being  able  to  make  better  use  of  the  tail 
end  of  the  pressure-volume  diagram. 

One  objection  is  that  explosions  at  constant  volume  have 
to  take  place  intermittently,  while  a  turbine  desires  a  contin- 
uous supply  of  fluid.  If  the  supply  is  not  continuous  the 
power  of  the  turbine  is  less  than  it  would  otherwise  be  for  a 
given  size  of  machine;  and  the  initial  cost,  the  bulk  and — 
most  important — the  loss  by  friction  are  greater  in  propor- 
tion to  the  power  developed  than  they  would  otherwise  be. 

The  other  objection  is  that  the  fluid  must  leave  the  explo- 
sion chamber  at  varying  pressure.  This  necessitates,  unless 
special  means'  are  provided  to  prevent  it,  the  fluid  entering 
the  turbine  casing  either  at  varying  pressure  or  at  varying 
velocity,  which  of  course  is  objectionable,  as  the  speed  of  ro- 
tation of  the  turbine  cannot,  during  the  period  of  a  cycle,  be 
made  to  vary  correspondingly. 

The  second  objection  might  be  met  by  employing  in  a  par- 
allel flow  turbine  of  the  De  Laval  type  long  radial  blades, 
and  causing  the  nozzles  to  be  altered  in  position  according  to 
the  pressure,  so  as  to  direct  the  gas  onto  the  outer  ends  of 
the  blades  at  low  pressures.  The  difficulty  could  also  be  met 
by  an  arrangement  of  reciprocating  engine  combined  with  a 
turbine,  the  gas  being  first  expanded  in  the  reciprocating 
engine  to  a  certain  pressure  and  then  passed  on  to  the  tur- 
bine to  complete  its  expansion.  If  several  reciprocating  cyl- 
inders were  employed,  the  first  objection  also  would  be  got 
over,  but  it  is  true  that  with  such  a  combination  some  of  the 
most  important  advantages  of  the  turbine  would  be  lost. 
The  idea  is,  however,  in  the  author's  opinion,  worthy  of  con- 


THE   GAS   TURBINE.  57 

sideration.     Reciprocating  steam  engines  have  been  success- 
fully combined  with  steam  turbines  in  this  manner.* 

Cycle  II,  Case  2. 

An  explosion  engine,  in  which  a  very  high  compression 
pressure  is  employed,  will  now  be  considered.  If  compres- 
sion be  carried  to  818  pounds  absolute  as  in  Cycle  I,  Case  4, 
one  obtains  with  a  maximum  temperature  of  2000°  C. 
(3632°  F.)  a  maximum  pressure  of  2045  pounds  absolute 
and  a  very  high  ratio  of  negative  work  to  gross  work.  If  a 
much  lower  compression  —  namely  417  pounds  absolute  —  is 
adopted,  this  will  give  a  temperature  of  compression  of  750° 
absolute  C.  (1382°  F.).  Working  on  the  same  cycle  as  in 
the  last  case  and  arranging  the  explosive  mixture  to  give  a 
maximum  temperature  of  2000°  C.  (2273°  absolute  C.),  a 
maximum  pressure  of  1265  pounds  absolute  is  obtained, 
and  the  pressure-volume  and  the  entropy-temperature  dia- 
grams will  be  as  shown  in  Figs.  23  and  24  (page  58). 

Referring  to  Fig.  24, 

, 
=U.DO. 


area  aUW  w 
Referring  to  Fig.  23, 

negative  work  _      area         ^ 
gross  work          area  u1UlUWWl 

E  is  the  same  as  in  Cycle  I,  Case  4,  and  the  ratio  of  negative 
work  to  gross  work  is  also  the  same.  The  compression  is 
lower  than  in  Cycle  I,  Case  4,  but  the  maximum  pressure,  is 
very  much  higher. 

The  excessively  high  maximum  pressure  is  an  objection 
to  this  case. 

*  See  Paper  by  Professor  Rateau  read  before  the  North  of  England  Insti- 
tute of  Mining  and  Mechanical  Engineers  at  Newcastle-on-Tyne,  Dec.  13,  1902; 
or  Paper  by  the  same  author  read  at  the  Chicago  Meeting  of  the  Institution  of 
Mechanical  Engineers,  Proceedings  1904,  Part  3  (page  737). 


58 


THE   GAS   TURBINE. 


T-2273 


FIG  24. — Cycle  II,  Case  2.     Temperature- 
entropy  diagram. 


Volume 


FIG.  23.-Cycle  II    Case  2.     Pressure- 
volume  diagram. 


THE   GAS   TURBINE.  59 

Cycle  II,  Case  2a. 

If  the  expansion  took  place  in  an  ideal  divergent  nozzle  as 
before  till  the  temperature  fell  to  700°  C.  (973°  absolute  C.), 
the  gas  would  still  have  a  pressure  of  70  pounds  absolute, 
while  the  mean  velocity  of  exit  from  the  nozzle  would  be 
4300  feet  per  second.  If  the  gas  were  expanded  in  the 
nozzle  down  to  25  pounds  absolute,  the  temperature  would 
then  be  741°  absolute  C.  (1366°  F.),  and  the  mean  velocity 
of  the  gas  leaving  the  nozzle  would  be  4830  feet  per  second. 

Cycle  III,  Case  1. 

It  has  been  proposed,  when  a  water-jacket  is  employed,  to 
utilize  the  heat  passed  into  the  jacket  water  by  causing  this 
heat  to  generate  steam  from  the  water.  This  steam  could 
then  receive  further  heat  from  the  products  of  combustion, 
which  would  therefore  be  reduced  in  temperature,  while  the 
steam  would  be  superheated.  The  steam  and  products  of 
combustion  could  then  expand  adiabatically,  doing  work  in 
the  same  or  in  separate  turbines.  The  carrying  out  of  this 
idea  would  affect  the  efficiency  in  the  several  cases  consid- 
ered of  Cycle  I.  Cooling  arrangements  are  not  required  in 
Cycle  I,  Case  1,  so  this  case  need  not  be  further  considered. 
In  Cycle  I,  Case  2,  let  it  be  supposed  that  the  combustion 
chamber  is  jacketed  and  that  the  jacket  water  is  heated 
and  converted  into  steam  by  heat  taken  from  the  products  of 
combustion,  which  have  their  temperature  thus  lowered  from 
2000°  C.  to  700°  C.,  that  is,  to  the  temperature  at  which  they 
can  safely  be  allowed  into  an  uncooled  turbine,  the  steam 
being  superheated  up  to  700°  C.  Let  this  be  called  Cycle 
III,  Case  1. 

Referring  to  Fig.  16  (page  41),  the  heat  in  the  products 
of  combustion  which  is  converted  into  work  is  now  repre- 
sented by  the  area  ABCD  instead  of  by  the  area  ABEF. 
The  heat  represented  by  the  area  dCEf  has,  however,  been 


60  THE   GAS   TURBINE. 

employed  in  heating  water  and  generating  and  superheating 
steam.  The  fraction  of  this  heat  which  is  converted  into 
work  will  not  now  be  as  great  as  in  the  original  scheme 
of  working.  That  is  to  say,  the  net  work  got  out  of  the  heat 
put  into  the  water  and  steam  will  be  less  than  the  area 
4 '  DCEF.  By  transferring  heat  to  the  water  and  steam  from 
the  gas,  E  is  therefore  reduced.  There  must,  however,  in  any 
case,  as  already  mentioned  (page  30),  be  lost  in  practice  a 
large  amount  of  heat  when  the  products  of  combustion  enter 
the  turbine  casing  at  a  temperature  such  as  2000°  C.,  and, 
by  adopting  this  combined  steam  and  gas  scheme,  a  much 
higher  practical  efficiency  may  possibly  be  attained  than 
would  otherwise  be  possible.  As  the  net  work  ideally  is  less 
than  in  Cycle  I,  Case  2,  and  as  the  negative  work  is  not  less 
(and  may  be  greater  by  the  amount  of  work  required  to 
pump  the  water  into  the  jacket  if  under  pressure),  the  ratio 
of  negative  work  to  gross  work  is  increased.  In  Case  2  of 
Cycle  I,  the  ratio  of  negative  work  to  gross  work  is  low,  and 
it  will,  therefore,  be  allowable  to  increase  this  ratio. 

Cycle  III,  Case  2. 

Case  3  of  Cycle  I  could  be  modified  in  the  same  way  by 
reducing  the  temperature  of  the  products  of  combustion  from 
2000°  C.  to  700°  C.,  and  by  employing  the  heat  so  given  up 
in  heating  water  and  generating  and  superheating  steam. 
The  steam  could  be  generated  at  300  pounds  pressure  ab- 
solute (the  same  pressure  as  the  products  of  combustion) 
and  superheated  to  700°  C.  at  this  pressure.  The  steam  and 
gas  could  then  be  expanded  adiabatically  in  the  same  or 
separate  turbines.  As  in  the  previous  case,  E  would  be 
reduced,  and  the  ratio  of  negative  work  to  gross  work 
increased.  As  in  the  previous  case,  the  practical  efficiency 
might  also  be  largely  increased. 

The  pressure-volume  and  entropy-temperature  diagrams 
for  the  gas  in  this  case  (called  Cycle  III,  Case  2)  are  shown 


THE   GAS   TURBINE. 


61 


in  Figs.  25  and  26  respectively  (pages  61  and  62).  The  gas  is 
compressed  along  the  line  AG  as  in  Cycle  I,  Case  3,  till  its 
pressure  is  300  pounds  absolute  and  its  temperature  is 
409.5°  C.  (682.5°  absolute  C.).  It  is  then  heated  by  com- 
bustion at  constant  pressure  along  the  line  GH  as  in  Cycle  I 
Case  3,  till  its  temperature  is  2000°  C.  (2273°  absolute  C.). 
Heat  is  now  withdrawn  from  the  gas  at  constant  pressure  and 
transformed  to  the  water  and  steam,  the  temperature  of  the 
gas  falling  along  the  line  HHlt  to  700°  C.  (973°  absolute  C.) 
at  Hr  The  heat  transferred  from  the  gas  to  the  water  is 


»-30O 
LV- 0-392 


K 


Volume 
FIG.  25. — Cycle  III,  Case  2.    Pressure-volume  diagram — gas. 

represented,  Fig.  26,  by  the  area  kJH^Hk.  The  gas  now  ex- 
pands adiabatically  along  the  line  H^K^  till  the  pressure 
is  15  pounds  absolute,  when  the  temperature  will  be  140°  C. 
(413°  absolute  C.).  The  contraction  of  the  gas  at  constant 
pressure  along  the  line  K^A  completes  the  cycle.  Dotted 
lines  have  been  placed  on  Figs.  25  and  26  to  illustrate  Cycle  I 
Case  3,  where  this  differs  from  the  present  cycle.  The  two 
cycles  can  thus  be  compared. 

Pressure-volume  and  entropy-temperature  diagrams  for 
the  water  are  shown  in  Figs.  27  and  28  (pages  63-65).  Re- 
ferring to  Fig.  28,  the  water  is  heated  at  a  constant  pressure 
of  300  pounds  per  square  inch  absolute  along  the  line  fc  from 


62 


THE   GAS   TURBINE. 


100.6°  C.  (373.6°  absolute  C.)  to  214°  C.  (487°  absolute  C.), 
which  is  the  boiling  point  at  this  pressure.  The  water  is 
now  converted  into  steam,  this  process  being  represented  by 
the  line  eg-,  and  the  steam  is  superheated  at  constant  pressure 
as  represented  by  the  line  gd,  till  its  temperature  is  700°  C. 


T-2273 


t-Z90 


a 

FIG.  26. — Cycle  III,  Case  2.    Entropy-temperature  diagram — gas. 

(973°  absolute  C.).  The  steam  is  then  expanded  adiabati- 
cally  along  the  line  de  till  it  falls  to  15  pounds  absolute 
pressure,  its  temperature  then  being  184°  C.  (457°  absolute 
C.).  The  steam  is  now  exhausted  and  cools  along  the  line 
eh.  At  h  it  is  saturated,  its  temperature  being  100.6°  C. 
(373.6°  absolute  C.),  and  thereafter  it  condenses  along  the 
line  hf  and  is  compressed  to  its  initial  state. 


THE   GAS  TURBINE. 


63 


Fig.  27  shows  the  work  done  by  the  steam  in  its  generation, 
superheating  and  adiabatic  expansion.  The  work  done  in 
forcing  the  water  into  the  chamber  at  300  pounds  pressure  is 
not  shown  in  Fig.  27  and  is  negligible  in  the  present  inves- 
tigation. 

The  heat  required  to  raise  the  water  from  373.6°  absolute 
C.  to  487°  absolute  C.,  is  represented  in  Fig.  28  by  the  area 
tjccv  The  area  c1cgg1  represents  the  latent  heat  of  steam 
at  a  pressure  of  300  pounds  absolute  (the  temperature  being 
487°  absolute  C.),  and  the  area  glgde1  represents  the  heat  re- 


•jrarr 

Volume 
FIG.  27. — Cycle  III,  Case  2.    Pressure-volume  diagram — steam. 

quired  to  superheat  the  steam  from  487°  absolute  C.  to  973° 
absolute  C.  The  area  fjhh^  represents  the  latent  heat  of 
steam  at  a  pressure  of  15  pounds  absolute,  and  the  area 
hlheel  represents  the  heat  required  to  superheat  this  steam 
from  373.6°  absolute  C.  to  457  absolute  C. 

Comparing  this  case  with  Case  3,  of  Cycle  I,  it  is  found 
that  the  total  heat  absorbed  is  the  same  in  both  cases,  being 
represented  by  the  area  aGHk  in  Fig.  26.  The  portion  of 
this  heat  which  is  converted  into  work  in  Case  3,  Cycle  I,  is 
represented  by  the  area  AGHK,  while  the  corresponding 
portion  in  the  present  case  is  represented  by  the  sum  of  the 
areas  AGH^K^  Fig.  26,  and  fcgdeh,  Fig.  28.  This  sum  is  less 


64  THE   GAS   TURBINE. 

than  the  area  AGHK,  and  E  in  this  case  is  only  0.33  as  com- 
pared with  0.58  in  Case  3  of  Cycle  I.  The  fall  in  the  value 
of  E  is  due  to  the  relatively  low  efficiency  of  the  steam  por- 
tion which  has  an  ideal  efficiency  of  only  0.28.  (For  a 
steam  engine  this  is  really  not  low.) 

The  feed-water  has  been  taken  at  a  temperature  corre- 
sponding to  atmospheric  boiling-point.  It  has  been  assumed 
that  the  steam  is  exhausted  into  the  atmosphere,  and  is  not 
condensed  for  use  over  again.  It  would,  therefore,  be  neces- 
sary, in  order  to  follow  the  cycle,  to  heat  the  feed-water  to 
100°  C.  It  should  not  be  difficult  to  approximately  accom- 
plish this  by  utilizing  the  heat  of  the  exhausting  gases. 
By  heating  the  feed-water  still  more,  the  efficiency  could 
be  improved;  but  the  improvement  would  be  slight  (less 
than  in  an  ordinary  steam  engine)  and  the  feed-water  would 
have  to  be  under  pressure.  As,  moreover,  any  increase  of 
exhaust  or  back  pressure  is  a  serious  matter  with  a  turbine, 
and  as  feed-water  heaters  must  to  a  certain  extent  affect 
this  back  pressure,  any  prospect  of  gain  by  heating  the  feed- 
water  beyond  100°  C.  need  not  be  considered. 

The  gross  work  in  the  present  case  is  represented,  Figs. 
25  and  27,  by  the  area  zZH^  +  the  area  acde.  This  is  less 
than  the  gross  work  in  Cycle  I,  Case  3,  which  is  represented 
by  the  area  zZHK.  The  negative  work  in  Cycle  I,  Case  3, 
was  represented  by  the  area  zZGA.  In  the  present  case  it 
is  also  represented  by  this  area,  neglecting  the  work  of  pump- 
ing the  water  into  the  jacket.  The  ratio  of  negative  work 
to  gross  work  in  the  present  case  is  0.41  as  compared  with 
0.3  in  Cycle  I,  Case  3.  This  ratio  (0.41)  is  rather  high.  It 
will,  however,  probably  not  be  so  objectionable  in  the  pres- 
ent case  as  the  ratio  0.40  in  Case  4  of  Cycle  III,  as  the  real 
efficiency  in  practice  will  come  nearer  to  the  ideal  in  this  case 
than  in  Case  4  of  Cycle  III.  In  the  present  case  the  ratio 
could  be  reduced  by  lowering  the  compression.  This  would 
reduce  E. 


THE   GAS   TURBINE. 


65 


As  the  mass  of  the  water  employed  is  not  the  same  as  the 
mass  of  the  air  and  fuel,  the  scale  for  entropy  in  Fig.  28 
has  been  made  different  from  that  in  the  other  entropy- 
temperature  diagrams,  so  that  in  all  these  diagrams  areas 
represent  quantities  of  heat  to  the  same  scale.  In  all  the 
pressure-volume  diagrams  the  scales  are  the  same  except  in 
Fig.  29  (page  66),  which  will  be  referred  to  hereafter.  It 
might  be  mentioned  here  that  all  the  numerical  results  given 
in  this  Paper  have  been  obtained  by  calculation  and  not  by 
scaling  the  diagrams. 

973  d 


373-6 


FIG.  28 — Cycle  III,  Case  2.    Entropy-temperature  diagram — steam. 

It  will  be  seen  that  it  has  been  assumed  that  the  gas  and 
steam  expand  adiabatically  separate  from  each  other.  The 
adiabatic  curve  of  the  one  is  different  from  that  of  the  other, 
as  the  specific  heats  are  different;  and,  while  the  gas  falls  to 
a  temperature  of  140°  C.  (413°  absolute  C.),  the  steam  falls 
only  to  184°  C.  (457°  absolute  C.).  This  will  be  correct  if  the 
steam  and  gas  are  not  mixed.  It  is  much  simpler  to  consider 
this  case  than  to  consider  the  case  where  the  gases  are 
intimately  mixed.  In  this  latter  case  the  diagram  Fig.  26 
would  be  altered,  and  it  could  not  so  easily  be  seen  where  the 
loss  of  efficiency  came  in.  In  practice,  however,  it  will  prob- 
ably be  found  convenient  to  mix  the  gases.  This  will  alter 
the  diagrams  and  the  efficiency  somewhat;  but  what  has 
been  considered  gives  a  good  idea  of  the  general  effect  of  the 
5 


66 


THE   GAS   TURBINE. 


employment  of  steam  in  conjunction  with  gas.  If  the  steam 
and  gas  are  not  mixed,  a  condenser  could  be  employed  for  the 
former.  The  steam  could  then  be  expanded  to  a  much  lower 
temperature  and  pressure,  and  the  efficiency  would  be  con- 
siderably raised. 

Cycle  II  could  be  modified  by  combining  steam  with  the 
gas,  in  the  same  way  as  Cycle  I  was  modified.  A  case  of  this 
nature  has  not  been  worked  out;  but  Case  1  of  Cycle  II 
could  probably  be  modified  in  this  way.  Case  2  of  Cycle  II 
could  not  be  so  treated  on  account  of  the  high  ratio  of  nega- 
tive work  to  gross  work  that  would  occur. 


10 


12 


14 


FIG.  29.  —  Pressure-volume  diagram.    The  horizontal  scale  is  half  that  of  the  other  diagrams. 

One  might  try  to  improve  on  all  these  cycles,  by  extending 
the  adiabatic  expansion  line  of  the  gas  below  atmosphere, 
instead  of  stopping  it  at  atmospheric  pressure.  It  would, 
of  course,  be  necessary  to  compress  the  fluid  back  again  to 
atmospheric  pressure;  but,  if  this  compression  were  isother- 
mal or  between  the  isothermal  and  adiabatic,  there  would 
be  an  increase  of  efficiency.  Carnot's  cycle  is  in  fact  being 
approached  in  the  lower  part  of  the  diagram. 

Figs.  29  and  30  are  respectively  pressure-volume  and 
entropy-temperature  diagrams  of  Cycle  I,  Case  3,  modified 
by  continuing  the  adiabatic  expansion  to  a  pressure  of  2 
pounds  per  square  inch  absolute.  The  scale  for  volumes  in 


THE   GAS   TURBINE. 


67 


Fig.  29  has,  for  convenience,  been  made  half  that  of  the  other 
diagrams.  Kb  represents  the  addition  to  the  adiabatic  line  of 
expansion,  and  be  represents  isothermal  compression  of  the 
gas  from  2  pounds  absolute  at  b  to  15  pounds  absolute  at  c. 
There  should  be  no  difficulty  in  a  turbine  in  extending  the 
expansion  from  K  to  b.  There  may  be  difficulty,  however,  in 


HT«2273 


/r-682-, 


(-290 


Ti»543 


1 

Vv\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\V\ 


FIG.  30. — Entropy-temperature  diagram. 

getting  isothermal  compression  from  b  to  atmospheric  pres- 
sure at  c.  As  the  volume  at  b  is  14  times  the  initial  volume 
it  will  be  desirable  to  get  the  fluid  discharged  as  quickly  as 
possible.  A  rotary  compressor  will  probably  be  best  for  this 
purpose.  A  compression,  sufficiently  near  to  the  isothermal 
and  sufficiently  remote  from  the  adiabatic  to  raise  the  effi- 
ciency appreciably,  should  be  obtainable. 


68  THE   GAS   TURBINE. 

The  temperature  at  b  is  270°  C.  (543°  absolute  C.),  and  if 
the  compression  were  isothermal,  this  would  of  course  be  the 
temperature  all  along  the  line  be.  The  gases  could  be  passed 
through  or  around  water-cooled  tubes  to  keep  down  the  tem- 
perature during  compression.  With  the  gas  at  a  temperature 
of  543°  absolute  C.  it  would  not  do  to  spray  water  into  it, 
unless  sufficient  water  were  sprayed  to  cool  the  gas  below  the 
boiling-point  of  the  water,  which  is  326°  absolute  C.  at  this 
pressure. 

If  compression  takes  place  along  the  isothermal  line  be,  a 
net  amount  of  work  will  be  gained,  represented  by  the  area 
Kbc.  The  gas  will  be  discharged  into  the  atmosphere  at  c, 
the  volume  at  discharge  being  1.874  of  the  original  volume 
(at  A).  Even  if  the  compression  is  not  isothermal,  an 
amount  of  work  may  be  gained  which  will  wipe  out  the  .extra 
losses  in  the  machine,  provide  for  pumping  out  the  cooling 
water,  and  perhaps  leave  a  margin  of  net  gain. 

In  Fig.  30  the  heat  absorbed  by  the  fluid  is  represented  by 
the  area  aGHk,  the  heat  rejected  by  the  area  aAcbk,  and  the 
heat  converted  into  work  by  the  area  AGHbc.  As  the  heat 
absorbed  remains  unchanged,  while  the  heat  converted  into 
work  is  increased  by  the  area  Kbc,  E  is  of  course  increased. 

__area  AGHbc 
~  area  AGHk 

This  enlarging  of  the  diagram  of  course  affects  the  ratio  of 
negative  work  to  gross  work.  Referring  to  Fig.  29  (page 
66), 

gross  work  =  area  zZHKebc 
negative  work  =  area  zZGA  +  area  Keb 
net  work  =  area  AGHbc 

negative  work  _  area  zZGA  +  area  Keb 
gross  work  area  zZHKebc 

In  the  free  piston  explosion  engines,  which  were  at  one 
time  in  fairly  common  use,  the  best  known  of  which  is  the 


THE   GAS  TURBINE.  69 

Otto  and  Langen,  the  expansion  was  carried  to  a  pressure 
considerably  below  the  atmosphere.  The  compression  to  at- 
mospheric pressure  which  followed  must  have  been  between 
the  isothermal  and  the  adiabatic. 

If  this  continuation  of  the  adiabatic  expansion  below  at- 
mospheric pressure  is  not  found  to  be  advisable  to  the  extent 
that  has  just  been  described,  it  may  be  found  advisable  to  a 
less  extent.  If  it  is  found  advisable  in  any  case,  it  is  more 
likely  to  be  so  in  a  case  in  which  the  high  pressure  of  the  gases 
after  combustion  is  reduced  to  a  low  pressure  in  divergent 
nozzles,  before  the  gas  is  allowed  into  the  turbine  casing, 
than  in  a  case  in  which  the  whole  fall  of  pressure  takes 
place  in  the  turbine  casing.  In  the  former  case  very  high 
vane  speeds  are  necessary,  and  the  friction  between  the 
rotating  parts  and  the  fluid  in  the  casing  is  an  extremely 
important  matter.  The  reduction  of  the  pressure  within  the 
turbine  casing  from  atmospheric  pressure  (or  above  that) 
to  one-quarter  or  one-eighth  of  that  amount  may  therefore 
very  much  reduce  the  frictional  losses.  It  is  true  that  the 
rotary  pump,  if  such  is  employed  for  completing  the  cycle, 
has  to  deliver  at  atmospheric  pressure,  but  the  rotating 
parts  of  the  pump  can  revolve  at  a  much  lower  speed,  and 
the  friction  will  therefore  be  of  much  less  consequence. 

With  such  high  speed  turbines  there  is  another  question  to 
be  considered.  It  has  been  stated  in  discussing  Cases  3a  and 
4a  of  Cycle  I,  and  la  and  2a  of  Cycle  II,  that  the  velocity 
of  the  gases  escaping  from  the  divergent  nozzles  would  be 
over  4000  feet  per  second,  if  the  heat  energy  converted 
into  kinetic  energy  was  as  mentioned.  The  author  is  not, 
however,  aware  of  any  results  of  experiments  having  been 
published  in  which  velocities  of  these  amounts  were  obtained, 
when  the  pressure  of  the  medium  into  which  the  divergent 
nozzle  discharged  was  atmospheric.  It  is  supposed  by  some 
that  there  is  a  maximum  limit  to  the  velocity  of  a  gas  leav- 
ing a  divergent  nozzle  and  escaping  into  a  given  medium 


70  THE   GAS   TURBINE. 

which  is  at  a  given  pressure,  etc.,  and  that  this  limit  velocity 
is  dependent  on  the  pressure  in  the  medium  into  which  the 
nozzle  discharges,  and  is  less  when  the  pressure  in  this  medium 
is  greater,  and  vice  versa.  That  is  to  say,  it  is  supposed  by 
some  that,  after  a  certain  velocity  of  discharge  has  been 
attained,  no  increase  in  the  initial  temperature  or  pressure 
will  increase  this  velocity;  but  a  reduction  of  the  pressure  in 
the  medium  may  do  so.  The  author  does  not  express  any 
opinion  himself  on  this  point,  but  if  it  should  be  found 
that  the  reduction  of  the  pressure  inside  a  turbine  casing 
below  atmospheric  pressure  enables  the  heat  energy  of  the 
gas  to  be  more  effectively  converted  into  kinetic  energy,  this 
will  be  a  further  argument  in  favor  of  so  reducing  the  pres- 
sure. Whether  or  not  there  is  an  advantage  to  be  gained 
remains  to  be  proved,  but  there  is  at  any  rate  a  possibility 
of  gain  by  thus  extending  the  expansion  and  it  is  a  possibility 
which,  in  the  author's  opinion,  should  not  be  ignored.  In 
dealing  with  large  volumes  and  small  pressures  there  is,  as 
already  mentioned,  an  immense  difference  between  turbines 
and  reciprocating  engines. 

Cycle  IV. 

The  fourth  cycle  which  will  be  considered  in  this  Paper  is 
one  in  which  a  high  ideal  efficiency  can  be  obtained  with  a 
low  compression,  and  without  having  an  abnormally  high 
ratio  of  negative  work  to  gross  work. 

Figs.  31  and  32  are,  respectively,  pressure-volume  and 
entropy-temperature  diagrams  for  an  engine  working  on 
this  cycle.  In  explaining  the  cycle  it  is  best  to  start  at  El. 
At  this  point  the  temperature  of  the  fluid  is  1592°  C.  (1865° 
absolute  C.),  and  the  pressure  is  30  pounds  absolute. 

Let  the  fluid  be  heated  by  combustion  at  constant  pressure 
along  the  line  ElCl  till  the  temperature  reaches  2000°  C. 
(2273°  absolute  C.).  Now  let  the  gas  expand  adiabatically 
from  C1  to  Dl  till  the  pressure  is  atmospheric.  The  tempera- 


THE    GAS   TURBINE.  71 

ture  will  then  be  1592°  C.  (1865°  absolute  C.).  Now  let  the 
gas  pass  through  a  regenerating  chamber  and  be  cooled  at  a 
constant  pressure  from  Dl  to  Fl  till  the  temperature  is  80°  C. 
(353°  absolute  C.)-  The  gas  escapes  at  Fl  into  atmosphere, 
and  thereafter  cools  at  constant  pressure  to  17°  C.  (290° 
absolute  C.)  at  A.  A  new  charge  is  taken  at  A  and  com- 
pressed adiabatically  to  B1  where  the  pressure  is  30  pounds 
absolute  and  the  temperature  80°  C.  (353°  absolute  C.). 
The  fluid  is  now  passed  through  the  regenerating  chamber, 
and  is  heated  at  constant  pressure  along  the  line  B1E\ 
taking  back  the  heat  given  up  by  the  last  charge.  This 
will  raise  its  temperature  to  1592°  C.  (1865°  absolute  C.)  and 
place  the  fluid  in  the  condition  it  was  at  the  start. 


FIG.  31.  —  Cycle  IV.    Pressure-  volume  diagram. 

Referring  to  Fig.  31,  the  gross  work  is  represented  by  the 
area  glGlClDl,  the  negative  work  by  the  area  glG1BlA)  and 
the  net  work  by  the  area  AB*C1D1. 

„,,        .         negative  work     area  Q1G1B1A 
Therefore—  _  =  -     _^=o.  16  (0.1553). 

gross  work        area  g*Gl€lDl 

The  heat  absorbed  by  the  fluid  (other  than  that  obtained 
in  the  regenerator  from  a  previous  charge)  is  represented  in 
Fig.  32  by  the  area  eElCld.  The  heat  rejected  (other  than 
that  given  to  the  regenerator)  is  represented  by  the  area 
aAF*f.  The  heat  converted  into  work  is  represented  by  the 
difference  of  these  two  areas. 


=  area  aBlC*d—  area  aBlEle  —  area  aAFlf 
=area  eE^d 


72 


THE   GAS   TURBINE. 


Therefore  the  area  AB1C1D1  represents  the  heat  converted 
into  work — 

•area 


Therefore 


area  eElCld 


0.84. 


The  ideal  efficiency  is  high;  but  the  highest  actual  effi- 
ciency which  could  practically  be  obtained  would  be  very 

fr=2273 


T,-I865 


\\V\\\\\\\\\\\\\\\\\\\\\\\\\ 


a       -f  e       <z 

FIG.  32. — Cycle  IV.    Entropy-temperature  diagram. 

much  below  this.  Besides  the  losses  in  the  motor  proper  and 
in  the  pump,  there  would  be  a  very  great  loss  in  the  regen- 
erator. It  would  not  be  practicable  to  reduce  the  tempera- 
ture of  the  exhausting  gases  in  the  regenerator  to  80°  C.,  or 
to  raise  the  temperature  of  the  fresh  gases  in  the  regenerator 
to  1592°  C. 


THE   GAS  TURBINE. 73 

If  the  losses  in  the  regenerator  and  in  the  passages  leading 
to  it  and  from  it  amounted  to  50  per  cent,  of  the  heat  which 
is  ideally  given  to  or  taken  from  the  regenerator,  these  losses 
would  have  to  be  made  up  by  extra  heat  given  to  the  fluid 
by  combustion,  and  the  efficiency  would  fall  to  0.3.  This 
does  not  take  into  account  the  losses  in  the  motor  proper 
and  in  the  pump.  The  heat  losses  in  the  motor  would 
probably  be  very  great.  This  cycle  may,  however,  when 
used  with  turbines,  give  results  sufficiently  good  to  justify 
its  use.  It  certainly  seems  to  promise  better  results  with 
turbines  than  with  reciprocating  engines,  on  account  of  the 
lower  frictional  losses  that  might  be  expected  with  turbines. 
With  reciprocating  engines  the  large  volumes  and  the  low 
pressure  of  the  fluid  would  cause  extremely  high  percen- 
tage losses  in  friction. 

The  cycle  has  the  disadvantage  that  gas  at  a  very  high 
temperature  has  to  be  conveyed  from  the  regenerator  to 
the  turbine.  This  practically  makes  it  absolutely  neces- 
sary to  have  the  turbine  quite  close  to  the  regenerator.  It 
would  seem  to  be  expedient  to  build  the  regenerator  of  brick- 
work and  to  erect  the  turbine  in  this  brick-work.  This  would 
very  much  limit  the  usefulness  of  the  cycle,  as  it  would  not 
be  quite  feasible  in  many  cases  to  have  either  a  regenerator 
of  the  nature  required  at  the  place  where  power  is  wanted, 
or  to  transmit  the  power  from  a  place  suitable  for  holding 
the  regenerator.  Nevertheless  there  will  be  cases  in  which 
it  will  be  quite  practicable  to  build  a  regenerator  beside  the 
turbine,  and  this  cycle  therefore  seems  to  be  worthy  of  con- 
sideration. A  rotary  pump  driven  from  the  turbine  spindle 
could  easily  be  used  for  compressing  the  gases,  thus  simpli- 
fying the  mechanical  moving  parts. 

The  several  cases  can  be  compared  in  the  Table  (page 
75).  It  will  be  seen  that  a  high  ideal  efficiency  is,  as  a 
rule,  accompanied  by  a  high  ratio  of  negative  work  to  gross 
work.  Cycle  4  is,  however,  an  exception  to  the  rule.  The 


74  THE   GAS  TURBINE. 

cycle  has  the  highest  ideal  efficiency  and  the  lowest  ratio  of 
negative  work  to  gross  work.  As  has  been  already  pointed 
out,  however,  the  efficiency  which  could  be  actually  looked 
for  with  this  cycle  would  be  very  much  below  the  ideal,  and 
the  cycle  has  other  objections,  as  already  stated. 

Cycle  I,  Case  1,  has  a  high  ratio  of  negative  work  to  gross 
work,  although  the  efficiency  is  the  lowest.  This  is  because 
all  the  heat  is  supplied  to  the  gas  at  a  comparatively  low 
temperature. 

Engineers  interested  in  any  particular  cycle  can  work  out 
other  cases  for  themselves  if  they  consider  it  necessary,  but 
it  is  suggested  that  after  a  careful  perusal  of  this  Paper  the 
effect  of  any  change  can  be  guessed  at  with  fair  accuracy. 
It  might  be  possible  to  use  the  exhaust  gases  from  a  turbine 
working  according  to  Cycle  I,  Cases  1  and  3,  or  Cycle  II, 
Case  1,  to  heat  the  fluid  after  compression  and  so  to  save 
fuel.  Consider  Fig.  14  (page  38).  The  heat  supplied  to 
the  fluid  is  represented  by  the  area  aBCd.  Part  of  this  heat 
might  be  obtained  from  the  hot  exhaust  gases  and  the 
efficiency  of  the  cycle  thus  raised,  as  will  be  clear  from  the 
description  just  given  of  Cycle  IV.  With  Cycle  I,  Cases  1 
and  3,  and  Cycle  II,  Case  1,  there  should  be  no  necessity 
to  use  a  regenerator  of  brick  or  such  like  refractory  material. 
The  exhaust  gases  could  be  passed  through  tubes  and  the 
fresh  air  passed  over  the  outside  surfaces  of  the  tubes,  or 
some  equivalent  construction  might  be  employed. 

Many  other  cycles  or  modifications  of  cycles  might  have 
been  investigated;  but  the  author  had  considered  it  inadvis- 
able to  burden  the  Paper  with  them. 

As  regards  the  Carnot  cycle,  an  engine  working  on  this 
cycle  would  have  the  same  value  for  E  as  one  working  on 
Cycle  I  for  the  same  values  of  t  and  tc',  and,  if  the  isothermal 
expansion  were  carried  far  enough,  it  would  (under  ideal 
conditions)  do  the  same  work  per  cycle  for  the  same  amount 
of  fluid,  and  have  the  same  ratio  of  negative  work  to  gross 


THE   GAS   TURBINE. 


75 


work.  The  maximum  volume  of  the  fluid  would,  however, 
be  very  much  greater;  and  although  this  is  not  such  a  serious 
matter  with  a  turbine  as  with  a  reciprocating  engine  it  is 
nevertheless  not  a  condition  to  be  accepted  without  due 
recompense. 

TABLE — Comparing  the  Several  Cycles  and  Cases. 


Cycle. 

Case. 

Compression. 

Maximum 
Temp, 
absolute 
C.° 

Maximum 
pressure 
Ibs. 
per  sq.  in. 
absolute. 

Ideal 
efficiency. 
(*) 

Ratio  of 
negative 
work 
to  gross 
work. 

Temp, 
absolute 
C.° 

Pressure 
Ibs. 
per  sq.  in. 
absolute. 

I 

1 

389 

42 

973 

42 

0.25 

0.40 

I 

2 

389 

42 

2273 

42 

0.25 

0.17 

I 

3&3a 

682.5 

300 

2273 

300 

0.58 

0.30 

I 

4  &  4a 

909 

818 

2273 

818 

0.68 

0.40 

II 

1  &  la 

500 

101 

2273 

459 

0.55 

0.23 

II 

2&2a 

750 

417 

2273 

1265 

0.68 

0.38 

III 

2 

682.5 

300 

2273 

300 

0.33 

0.41 

IV 

— 

353 

30 

2273 

30 

0.84 

0.16 

If  an  engine  working  on  Cycle  I  has  Tl  =tc,  then  an  engine 
working  on  the  Carnot  cycle  with  the  same  values  of  t  and  tc 
would  require,  in  order  to  do  the  same  work,  to  commence 
its  adiabatic  expansion  at  the  point  where  the  engine  working 
on  Cycle  I  leaves  off.  If  p  and  P1  on  the  Cycle  I  engine  are 
atmospheric  pressure,  then,  on  the  Carnot  cycle  engine,  the 
whole  of  the  adiabatic  expansion  would  take  place  below 
atmospheric  pressure.  It  is  interesting  to  compare  the  Car- 
not cycle  with  other  cycles,  but  it  hardly  seems  useful  in  the 
present  investigation  to  devote  any  more  space  to  this  com- 
parison. 

Although  the  practical  efficiency  of  an  engine  is  usually  of 
great  importance,  there  are  many  occasions  on  which  a  very 
poor  efficiency  will  be  tolerated  if  other  conditions  are  satis- 
factory. Small  gas  engines  using  lighting  gas,  costing  2s.  to 
3s.  per  1000  cubic  feet,  are  employed  in  great  numbers,  al- 
though the  fuel  cost  per  brake  horse-power  hour  is  very  high. 


76  THE   GAS  TURBINE. 

Small  electro-motors  are  extensively  used  consuming  cur- 
rent which  costs  over  2d.  per  Board-of-Trade  Unit  (kilo- 
watt-hour). The  fuel  cost  and  the  energy  cost,  respectively, 
in  the  two  cases  are  high;  but  the  user  prefers  to  put  up 
with  this,  rather  than  employ  a  power  plant  which  has  a 
higher  initial  cost  or  which  requires  more  attention  or  is 
generally  more  inconvenient. 

If,  therefore,  small  gas  turbines  could  be  sold  at  a  low 
price,  and  if  they  required  little  attention  and  did  not 
readily  get  out  of  order,  they  might  be  in  great  demand,  even 
although  the  gas  consumption  per  brake  horse-power  hour 
was  high.  With  the  average  user  of  a  small  engine,  produc- 
ing say  100  brake  horse-power  hours  per  week,  a  reduction 
of  10£  in  the  initial  cost  is  of  more  consequence  than  a  re- 
duction of  2  cubic  feet  per  brake  horse-power  hour  in  gas 
consumption.  The  same  user  would  no  doubt  be  quite 
willing  to  allow  an  additional  5  cubic  feet  of  gas  per  brake 
horse-power  hour  if  he  were  saved  trouble  and  anxiety  and 
small  expenses  in  the  working  of  the  engine. 

To  produce  a  gas  turbine  cheaply  it  seems  necessary 
to  avoid  reciprocating  parts  entirely  and  to  be  content  with 
a  low  compression.  Cycle  I,  Case  1,  appears  to  lend  itself 
to  cheapness  of  construction  and  simplicity,  but  it  might 
be  advisable  to  reduce  the  compression  at  the  expense  of 
efficiency.  A  rotary  pump  could  undertake  the  compres- 
sion. 

In  many  cases  the  vibration  of  a  reciprocating  engine  is 
extremely  objectionable;  and  a  motor  that  ran  with  practi- 
cally no  vibration  would  be  popular,  even  if  its  initial  cost 
were  greater  and  it  were  more  extravagant  with  fuel.  In 
motor  cars,  for  example,  oil  or  spirit  explosion  engines  are 
used  for  their  lightness  and  compactness;  but  the  vibration 
they  cause  is  objectionable.  If  a  satisfactory  turbine  were 
obtainable,  there  is  no  doubt  that  motor-car  builders  would 
eagerly  buy  it  and  install  it  on  their  cars,  even  if  the  cost 


THE   GAS  TURBINE. 77 

were  greater  and  the  efficiency  less  than  the  many  arrange- 
ments of  explosion  reciprocating  engines  now  in  use. 

One  might  mention  many  other  uses  to  which  gas  tur- 
bines could  advantageously  be  put,  if  they  were  obtainable 
as  fairly  efficient  and  reliable  machines.  In  many  factories 
and  engineering  works,  electric  motors  fed  by  current  from 
a  central  station  are  used  to  drive  individual  machines  or 
groups  of  machines,  in  order  to  save  the  losses  and  inconven- 
iences produced  by  driving  by  belts  or  ropes.  Gas  engines 
(reciprocating)  have  been  used  to  a  limited  extent  for  the 
same  purpose;  but  the  foundations  required  for  these  and  the 
vibration  caused  by  them  have  prevented  their  extensive 
use.  If  a  gas  turbine  were  obtainable  which  could  be  set 
down  anywhere  like  an  electric  motor,  it  would  serve 
splendidly  for  this  purpose,  and,  in  order  to  displace  electric 
driving,  it  would  only  require  to  possess  an  efficiency  greater 
than  the  efficiency  of  the  central  station  engine  multiplied 
by  the  efficiencies  of  dynamo,  mains,  and  motor. 

Suction  gas  producers  are  coming  into  extensive  use,  and 
by  their  means  gas  engines  can  take  the  place  of  steam  en- 
gines where  they  otherwise  would  not.  Whatever  objections 
there  might  be  to  the  supply  of  gas  to  gas  engines  from  these 
suction  producers,  these  objections  should  be  less  rather  than 
greater  with  turbines  than  with  reciprocating  engines. 

The  power  of  a  gas  turbine  could  be  effectively  varied  with 
an  insignificant  variation  of  speed,  by  cutting  out  one  or 
more  of  the  nozzles  or  admission  ports  which  admit  the  fluid 
to  the  turbine  buckets  or  first  set  of  buckets  when  several 
are  employed  in  series,  the  fluid  being  passed  through  the 
acting  ports  or  nozzles  at  a  uniform  pressure  and  with  a 
uniform  velocity.  To  enable  the  acting  nozzles  or  admis- 
sion ports,  no  matter  how  many  may  be  in  use,  to  deliver 
the  fluid  always  in  the  same  uniform  manner,  it  will  be 
necessary,  if  one  flame  supplies  all  the  nozzles  or  admission 
ports,  to  control  the  fuel  and  air  supplies  to  the  flame  in  con- 


78  THE   GAS   TURBINE. 

junction  with  the  mechanism  which  cuts  off  the  nozzles  or 
admission  ports.  It  will,  however,  be  usually  advisable  to 
supply  the  air  and  fuel  to  the  flame  at  a  constant  velocity 
which,  although  it  could  be  done  when  one  flame  supplied 
a  varying  number  of  nozzles,  would  involve  complications; 
and  it  may  therefore  be  found  expedient  to  have  a  separate 
flame  and  a  separate  combustion  chamber  for  each  nozzle. 
This  would  involve  the  necessity  of  igniting  or  extinguishing 
a  flame  for  each  change  of  power,  and,  although  this  could 
be  done  automatically,  it  is  objectionable.  Much  careful 
consideration  will  be  required  to  determine  which  is  the  least 
evil  to  put  up  with  and  which  course  had  best  be  taken. 

The  author  hopes  that  this  comparison  of  the  several 
cycles  treated  will  be  of  some  use  in  showing  what  may  be 
expected  from  each,  and  which  will  be  best  suited  for  a  motor 
which  is  required  to  work  under  given  conditions  and  which 
it  is  important  should  have  given  characteristics.  One 
cannot,  however,  compare  the  several  cycles  and  estimate 
the  actual  efficiencies,  &c.,  which  might  be  expected  in  prac- 
tice in  anything  like  so  satisfactory  a  manner  as  could  be 
desired,  without  having  more  information  obtained  by  ex- 
periment on  the  following  three  points : — 

1.  Losses  in  pneumatic  compression  to  high  pressures. 

(a)   With  reciprocating  compressors. 
(6)  With  rotary  compressors, 
(c)  With  a  combination  of  reciprocating  and  ro- 
tary compressors. 

2.  Expansion  of  hot  gases  in  divergent  nozzles. 

3.  Radiation  losses  and  transference  of  heat  from  gases 
to  metals  at  high  temperatures. 

It  would  immensely  aid  the  solving  of  the  gas  turbine 
problem  if  a  thorough  set  of  experiments  on  these  three 
points  were  made  and  the  results  published.  This  would 
naturally  cost  a  considerable  amount  of  money;  but  the 
information  obtained  by  the  engineering  world  would  be 


THE   GAS   TURBINE.  79 

very  good  value  at  the  price.  Money  has  been  spent  and  is 
being  spent  by  engineering  and  scientific  societies  on  inves- 
tigations which,  while  no  doubt  interesting  and  instructive, 
are  not  of  so  far-reaching  importance  as  experiments  which 
would  materially  aid  in  the  production  of  a  successful  gas 
turbine. 

Discussion. 

The  PRESIDENT  said  that  the  author  of  the  Paper  had 
been  for  a  long  time  associated  with  Mr.  Dugald  Clerk.  It 
was  rather  an  exception  for  the  Council  of  the  Institution  to 
accept  a  Paper  based  upon  theoretical  considerations  alone, 
the  rule  being  to  reject  Papers  unless  they  were  founded 
upon  something  that  had  actually  been  accomplished  in  a 
concrete  form.  But  he  thought  the  large  audience  before 
him  that  evening  justified  the  Council  in  having  admitted  the 
present  Paper  for  theoretical  discussion.  With  the  American 
Society  of  Mechanical  Engineers  no  formal  vote  of  thanks 
was  passed  for  a  Paper.  Thus  time  was  saved  for  the  techni- 
cal discussion.  The  procedure  of  this  Institution  had  latterly 
followed  the  same  course,  and  the  appreciation  of  the  present 
Paper  might  now  be  indicated  by  a  round  of  applause. 

Mr.  NEILSON  said  there  were  many  methods  of  working 
and  devices  suggested  in  the  Paper  which  had  been  pre- 
viously proposed,  some  of  them  over  and  over  again.  It  was 
extremely  difficult  in  many  cases  to  ascertain  to  whom  the 
credit  was  really  due  for  those  devices  or  methods  of  work- 
ing, and  therefore  he  had  in  most  cases  refrained  from  giving 
acknowledgment  to  any  one.  He  mentioned  that  fact  in 
case  any  one  should  feel  aggrieved  at  not  being  given  the 
credit  of  something  stated  in  the  Paper.  He  wished  to  em- 
phasize what  he  had  said  at  the  beginning  of  the  Paper — 
that  its  most  important  object  was  to  draw  opinions  from 
other  engineers  who  had  studied  the  question,  and  especially 
from  those  who  had  conducted  experiments. 


80 


THE   GAS  TURBINE. 


Mr.  HENRY  DAVEY,  Member  of  Council,  said  he  had 
made  some  experiments,  but  they  had  been  on  a  small  scale, 
and,  with  a  view  to  starting  the  discussion,  he  would  just 
state  what  his  experience  had  been.  First  of  all  he  would 
like  to  tender  his  thanks  to  the  author  for  bringing  the  Paper 
before  the  Institution.  It  dealt  with  an  important  subject. 
When  a  Paper  was  brought  before  engineers,  and  the  theory 
of  the  subject  was  put  before  them  so  lucidly  as  it  had  been 
put  by  the  author,  it  encouraged  them  to  look  more  minutely 
into  the  matter,  and  to  see  if  some  practical  good  might  not 
come  out  of  it.  The  Paper  was  valuable  as  indicating  the 


Non-Return 


\y**uy  fluid 


ira/ve  ^ 

^~] 

t 
f 

1 

Air 

E^ 

—  _: 

^ 

1 

nnr 

zn: 

Gas- 

Hi 

\ 

4      \ 

\  /&*£ 

% 

'/  , 

\ 

/ 

% 

I 

W//A 

I 

w// 

& 

FIG.  33. — Experimental  working  fluid  producer. 

direction  in  which  the  possibilities  of  the  problem  lay.  The 
first  part  of  the  problem  was  that  of  producing  in  a  practical 
way  the  working  fluid;  then  the  temperature  difficulties 
followed,  and  they  must  be  succeeded  by  the  mode  of  appli- 
cation to  the  turbine. 

It  was  from  the  point  of  view  of  producing  the  working 
fluid  that  he  had  made  two  or  three  experiments,  on  quite 
a  small  scale.  They  were  undertaken  with  an  apparatus, 
shown  in  Fig.  33,  based  on  Cycle  III,  Case  2  (page  60). 
A  was  a  combustion  chamber  lined  with  fire-brick,  and 
above  it  was  a  small  steel  boiler  consisting  of  a  shell  contain- 
ing the  water,  having  fire-tubes  B  extending  to  the  smoke- 


THE   GAS   TURBINE.  81 


box  or  vessel  C.  A  non-return  valve  opened  into  the  smoke- 
box.  When  steam  was  raised  above  the  pressure  in  the 
furnace,  it  passed  through  the  valve  and  mixed  with  the 
products  of  combustion.  The  object  of  the  apparatus  was 
to  produce  a  mixture  of  steam  and  products  of  combustion, 
the  steam  being  highly  superheated.  The  furnace  was  fed 
by  means  of  gas  and  air  pumps,  of  the  relative  capacities  for 
delivering  a  burning  mixture.  The  gas  and  air  were  deliv- 
ered in  separate  pipes  and  came  together  just  inside  the 
furnace.  To  start  the  apparatus  it  was  necessary  to  get  the 
fire-brick  lining  into  a  red-hot  state,  so  that  it  might  main- 
tain combustion;  then  the  air  and  gas  pumps  were  put  to 
work.  He  experimented  with  this  apparatus  on  a  small 
scale,  but  he  found  many  practical  difficulties.  He  com- 
menced with  low  pressures,  intending  to  go  on  step  by  step 
to  higher  and  higher  pressures;  but  what  happened  was  that, 
if  the  gases  ceased  to  burn  in  the  furnaces  from  any  acci- 
dental cause  during  one  or  two  strokes  of  the  pump,  then  a 
big  explosion  frequently  ensued.  It  seemed  to  him  that  the 
system  promised  well,  if  the  practical  difficulties  of  keeping 
the  combustion  constant  could  be  overcome.  If  the  diver- 
gent nozzle  was  as  efficient  as  one  might  imagine,  it  might 
be  that  a  turbine  worked  with  a  fluid  produced  from  an 
apparatus  of  that  kind,  at  moderately  low  pressure,  would 
give  a  good  efficiency;  but  the  loss  of  efficiency  in  the  air 
and  gas  pumps  would  be  considerable.  His  pumps  were 
reciprocating;  and  the  loss  would  be  probably  much  more 
considerable  if  they  were  rotary  ones.  That  would  tell  very 
much  against  the  scheme,  as  it  was  all  a  question  of  what 
useful  work  could  be  got  out  of  a  given  quantity  of  gas. 
Instead  of  bringing  air  and  gas  from  the  furnace  into  the 
combustion  chamber  to  be  burnt  with  a  constant  flame,  he 
altered  the  apparatus  as  shown  at  D.  The  gas  and  air  united 
together  in  the  pipe  e  and  pushed  forward  the  products  of 
combustion  of  the  last  charge,  forming  a  kind  of  cartridge 

6 


82  THE   GAS   TURBINE. 

in  the  pipe.  Then  the  supply  was  cut  off,  and  a  sparking 
plug  at  once  fired  the  cartridge.  With  a  moderate  sized 
brick-lined  chamber  A,  a  fairly  constant  pressure  could  be 
kept  up.  The  cartridge  might  be  small  and  fired  very  fre- 
quently, or  three  or  four  of  them  might  be  used  and  fired 
intermittently,  to  avoid  intermittent  impulses  on  the  tur- 
bine. He  had  not  got  beyond  what  might  be  termed  labora- 
tory experiments,  but  had  succeeded  in  getting  the  thing 
to  work  fairly  at  a  low  pressure.  He  had  not  used  the  work- 
ing fluids  to  propel  a  turbine,  but  he  had  taken  them,  in  the 
particular  case  he  mentioned,  into  a  reciprocating  engine. 
It  was  desirable  to  know  what  were  the  losses  due  to  com- 
pression both  with  reciprocating  and  rotary  pumps,  and 
then  came  the  very  great  difficulties  of  using  high  tempera- 
tures in  the  turbine  itself.  With  regard  to  the  divergent 
nozzle,  there  was,  as  far  as  he  knew,  scarcely  any  practical 
information  available.  It  was  one  of  those  subjects  which 
required  to  be  thrashed  out  experimentally,  and  one  of  the 
most  important  points  in  connection  with  the  development 
of  the  gas  turbine. 

Professor  F.  W.  BURSTALL  said  it  was  a  source  of  great 
gratification  to  him  to  be  able  to  attend  and — he  would  not 
say  discuss  the  Paper,  because  it  was  not  a  Paper  which 
admitted  of  a  great  deal  of  discussion — speak  on  a  subject 
which  was  one  of  immense  possibilities  and  potentialities. 
It  might  not  be  for  the  present  generation  to  inherit  the  gas 
turbine,  but  it  was  probable  that  it  would  come  to  subse- 
quent generations.  If  he  might  say  one  word  of  criticism  in 
regard  to  the  Paper,  he  thought  perhaps  the  author  was  a 
little  optimistic  on  the  subject.  He  knew  very  well  the 
enormous  difficulties  which  stood  in  the  way  of  a  commer- 
cial gas  turbine.  From  the  days  of  Watt  it  had  taken  nearly 
120  years  to  develop  a  comparatively  simple  thing  like  the 
steam  turbine,  and,  when  it  was  considered  that  the  gas 


THE   GAS   TURBINE.  83 

turbine  had  not  got  to  turn  the  energy  of  the  fluid  into 
kinetic  energy  on  the  shaft,  but  had  to  compress  the  fluid, 
to  ignite  the  fluid,  and  deal  with  a  fluid  which  was  infinitely 
more  troublesome  to  deal  with  than  steam,  it  would  be  3een 
what  difficulties  had  to  be  overcome.  He  did  not  for  a  mo- 
ment say  that  a  gas  turbine  could  not  be  made;  perhaps  he 
would  plead  guilty  to  having  schemed  a  good  many  himself. 
There  was  no  difficulty  in  making  one;  the  difficulty  was  to 
make  a  turbine  which  would  produce  any  useful  work  at  the 
engine  shaft,  and  for  a  reason  which  be  would  very  soon 
make  clear.  In  the  Otto  cycle  engine  the  compression  was 
produced  almost  entirely  in  the  motor  cylinder  itself,  and 
therefore  any  heat  which  escaped  from  the  charge  of  air  and 
gas  into  the  walls  of  the  cylinder  was  only  there  for  a  short 
time,  if  at  all.  When  the  charge  exploded,  the  cylinder  walls 
were  heated,  and  cooled  on  exhaust,  but  at  any  rate  they 
were  probably  very  much  above  the  temperature  of  the  com- 
pression charge.  It  was  clear,  he  thought,  that  no  turbine 
could  ever  be  made  to  work  on  that  principle.  The  com- 
pression of  the  air  and  gas  must  take  place  outside  the  tur- 
bine casing.  Therefore  one  had  to  contemplate  the  possibil- 
ity of  economically  producing  that  compression. 

The  author  had  alluded  to  the  rotary  compressor.  The 
rotary  compressor,  as  far  as  he  knew  it — and  that  was  only 
up  to  about  7  pounds  or  8  pounds  per  square  inch — was 
singularly  inefficient,  and  he  felt  convinced  that  any  rotary 
compressor  at  present  known  would  take  the  whole  power 
of  the  engine  to  compress  the  air  and  gas  to  begin  with, 
because  its  efficiency  was  probably  not  more  than  0.4;  and, 
when  it  was  considered  that  the  negative  work  was  0.4,  it 
would  be  found  there  was  about  30  per  cent,  of  the  work  of 
the  engine  absorbed  in  compression.  Referring  to  the  exper- 
iment of  Diesel,  by  taking  a  portion  of  the  air  during  com- 
pression and  compressing  it  in  an  independent  cylinder,  a 
very  much  higher  efficiency  had  been  obtained.  On  that 


84 THE   GAS   TURBINE.        . 

point  he  could  answer  the  question  with  regard  to  the  effi- 
ciency which  Diesel  got  in  his  compression  cylinder.  The 
pressures  were  not  correctly  stated  in  the  Paper,  though 
perhaps  they  were  the  pressures  found  by  Mr.  Ade  Clark. 
In  his  own  Diesel  engine  the  compression  in  the  cylinder 
was  35  atmospheres,  and  the  compression  on  the  blast  used 
for  spraying  the  oil  was  57  atmospheres.  The  efficiency  in 
the  small  compressor  was  not  high,  but  then  that  small 
compressor  took  such  a  very  small  charge  that  it  did  not 
affect  the  general  efficiency  of  the  Diesel  engine,  or  hardly 
appreciably. 

When  dealing  with  the  steam  engine,  one  was  dealing 
with  a  fluid  that  could  be  carried  over  very  large  distances 
without  very  much  loss  of  heat.  A  5  per  cent,  liquefaction 
in  a  pound  of  dry  steam  would  liberate  quite  a  considerable 
quantity  of  heat.  In  the  gas  engine,  however,  those  condi- 
tions were  reversed.  Any  fall  of  temperature  of  the  gas 
came  entirely  from  the  internal  energy  of  the  gas,  and  there- 
fore an  explosion  charge  could  not  be  trusted  to  remain  in 
contact  with  the  metallic  surface  for  any  length  of  time 
without  an  excessive  loss  of  heat.  From  that,  he  inferred 
that  any  form  of  Parsons  turbine  was  not  the  most  desirable 
form  for  working  with  gases.  The  cooling  in  passing  through 
the  comparatively  small  passages  would  be  so  immensely 
rapid  as  to  prevent  anything  like  -a  reasonable  efficiency 
being  obtained.  In  the  reciprocating  engine  there  was  a 
rather  different  set  of  conditions.  There  was  a  large  volume 
of  gas  in  a  cylindrical  vessel,  and  only  the  outer  portion  of  it 
became  cooled  at  all,  the  centre  core  remaining  always  hot, 
there  being  not  sufficient  time  to  pass  its  heat  to  the  outer 
walls.  Hence  the  losses  from  cooling  in  a  reciprocating 
engine  were  not  serious. 

With  regard  to  the  possibility — and  he  was  afraid  it  was 
the  only  possibility  in  the  last  instance — of  using  the  diver- 
gent nozzle,  the  author  had  clearly  indicated  what  were  the 


THE   GAS   TURBINE.  85 

limiting  conditions  for  that  divergent  nozzle,  namely,  that 
a  velocity  was  required  of  about  5200  feet  per  second  in 
order  to  turn  the  heat  energy  of  the  charge  into  the  kinetic 
energy  of  the  turbine  vanes.  Probably,  at  present,  that  was 
not  possible,  but  he  saw  no  reason  whatever  to  suppose  that, 
with  the  advances  in  metallurgical  science,  engineers  would 
not  be  in  possession  of  a  material  which  would  stand  the 
high  stresses  and  which  might  probably  be  lighter.  It 
seemed  to  him  by  no  means  impossible  to  get  that,  and, 
granting  the  fact  of  a  material,  then  the  turbine  was  mate- 
rialized almost  at  once.  It  was  a  matter  of  mechanical  dif- 
ficulties. As  he  had  stated  before,  there  was  no  reason  to 
suppose  that  it  would  be  anything  like  economical,  owing 
to  the  very  high  ratio  of  the  negative  work,  which  did  not 
occur  with  the  reciprocating  engine. 

The  questions  which  the  author  raised  with  regard  to 
data  were  of  course  extremely  important,  particularly  the 
questions  relating  to  the  reciprocating  compressor  and  the 
expansion  of  hot  gases  in  the  divergent  nozzle.  The  author 
would  probably  know  very  well  that  any  one  of  those  exper- 
iments was  a  most  serious  matter  to  undertake,  and  to  get 
results  which  were  in  any  way  commensurate  with  practical 
work  meant  conducting  the  experiments  on  a  large  scale. 
When  experiments  such  as  those  were  conducted  on  a  large 
scale  the  expenses  were  apt  to  be  enormous,  and  therefore 
one  could  hardly  expect  any  private  individual  to  give  his 
information  for  the  good  of  the  world  at  large.  If  the  experi- 
ments were  made,  no  doubt  they  would  be  made  by  some 
individual  who,  naturally,  was  seeking  his  own  advance- 
ment and  who  wished  to  produce  a  commercial  article. 
Whether  such  a  thing  was  possible  he  did  not  know,  but  he 
felt  very  strongly  there  was  no  possibility  of  advance  in  that 
direction  until  more  efficient  compressors  were  obtained. 
That  was  the  real  gist  of  the  matter.  In  the  last  five  years 
he  had  had  on  the  average  from  six  to  eight  patents  for  gas 


86  THE   GAS  TURBINE. 

turbines  put  before  him,  and  in  every  case  he  had  discovered 
that  they  were  perfectly  vague  on  the  subject  of  the  nega- 
tive work.  If  the  author  only  succeeded  in  persuading  engi- 
neers that  that  was  the  real  rock  on  which  they  split  in  devis- 
ing a  gas  turbine,  then  he  thought  the  object  of  the  Paper 
would  be  thoroughly  accomplished.  He  thanked  the  author 
for  having  brought  such  a  subject  before  the  Institution, 
even  if  it  were  only  in  the  form  of  a  scientific  investigation. 

Mr.  JAMES  ATKINSON  said  the  author  had  given  a  most 
excellent  Paper  on  the  theory  of  gas  turbines,  and  as  a  mat- 
ter of  fact  the  gas  turbine  simply  existed  now  in  theory. 
Whether  it  would  remain  so  or  not  was  a  question  that  might 
take  a  good  deal  of  deciding.  With  regard  to  the  tempera- 
ture which  the  author  assumed  could  be  put  into  a  turbine 
of  the  Parsons  type,  the  author  had  taken  it  as  700°  C. 
(1292°  F.).  Professor  Burstall  had  spoken  about  the  prob- 
abilities of  a  metal  which  would  stand  those  temperatures 
and  the  scouring  action  which  must  take  place  in  a  turbine, 
but  he,  Mr.  Atkinson,  thought  such  a  metal  was  a  long  way 
from  being  discovered.  Any  metal  that  had  iron  in  its  com- 
position commenced  to  oxidize  at  about  400°  C.  (752°  F.), 
or  500°  less  than  the  temperature  given  by  the  author.  If 
that  temperature  existed  in  the  presence  of  free  oxygen, 
metal  would  begin  to  oxidize,  and  the  scouring  action  which 
took  place  in  the  turbine  would  very  soon  wash  away  the 
blades.  He  thought  the  author  might  have  made  a  slight 
mistake  in  talking  about  superheated  steam  in  steam-engines 
and  the  efficiency  being  only  a  small  percentage.  As  a  mat- 
ter of  fact,  he  thought  superheating  in  the  steam  engine 
was  more  efficient  than  the  actual  steam  working  in  the 
steam  engine.  In  a  turbine,  superheating  the  steam  in- 
creased the  efficiency  very  largely,  and  it  would  increase  the 
efficiency  of  a  steam  engine  equally  as  well,  if  it  were  not  for 
the  fact  that  superheated  steam  went  a  very  small  way 
through  a  steam  engine,  and  in  a  triple-expansion  engine  it 


THE   GAS   TURBINE.  87 

very  rarely  went  beyond  the  high-pressure  cylinder,  if  as  far 
as  that.  He  expressed  his  admiration  for  the  care,  atten- 
tion, and  trouble  the  author  had  taken  in  producing  his  cal- 
culations, which  would  be  of  very  great  use  to  engineers  who 
had  to  deal  with  the  question.  The  Paper  practically  did  for 
the  gas  turbine  what  Mr.  Dugald  Clerk  did  for  the  gas 
engine  many  years  ago. 

Lt.-Colonel  R.  E.  B.  CROMPTON,  C.B.,  thought  that  the 
two  great  difficulties  which  stood  in  the  way  of  producing  a 
gas  turbine  had  been  fully  stated  by  Mr.  Davey  and  Pro- 
fessor Burstall,  the  latter  of  whom  had  rounded  up  the  sub- 
ject so  completely  that  it  left  little  for  others  to  say.  There 
was  one  point,  however,  which  might  perhaps  be  mentioned, 
although  he  was  uncertain  whether  it  could  be  fairly  dis- 
cussed under  the  question  of  gas  turbines.  He  had  recently 
been  present  at  the  Electrical  Congress  at  St.  Louis,  and  had 
taken  part  in  the  discussions  which  followed  two  interesting 
Papers,  read  by  Mr.  Emmett,  of  the  General  Electric  Co., 
of  Schenectady,  on  the  Curtis  form  of  steam  turbine,  and  by 
Mr.  Hodgkinson,  of  the  Westinghouse  Co.,  of  Pittsburg,  on 
the  Parsons  form  of  steam  turbine.  Several  speakers  ap- 
peared to  think  that  one  method  of  obtaining  the  maximum 
efficiency  in  electrical  energy  from  the  energy  in  the  coal 
would  be  by  using  the  gas  producer  and  gas  engine  to  deal 
with  the  higher  temperatures,  and  by  utilizing  the  energy 
remaining  in  the  jacket-cooling  water  and  in  the  exhaust  of 
the  gas  engine  by  raising  steam  in  a  suitable  boiler  and  util- 
izing this  steam  in  a  low-pressure  steam  turbine.  In  this 
way  it  seemed  possible  to  increase  the  present  highest  prac- 
tical efficiency  obtainable  with  the  gas  engine  from  the 
figure  of  about  28  per  cent,  up  to  possibly  38  per  cent.  He 
thought  that  there  were  no  practical  difficulties  in  the  way 
of  the  mechanical  engineer  in  carrying  out  this  development. 
What  would  then  remain  to  be  considered  would  be  whether 
the  economical  advantage  in  increased  efficiency  would  not 


88  THE   GAS   TURBINE. 

be  more  than  counterbalanced  by  the  extra  first  cost  and 
afterwards  by  the  maintenance  cost  of  the  extra  plant  that 
would  have  to  be  added  to  obtain  this  increased  duty  from 
the  fuel.  It  appeared  to  him  that,  in  many  cases  where  fuel 
was  dear,  it  was  quite  probable  that  the  answer  would  be 
favorable,  and  that  therefore  such  a  proposition  ought  to 
be  seriously  taken  in  hand  by  those  interested  in  the  ques- 
tion. Speaking  as  a  power  engineer,  he  thought  that  this 
combined  use  of  gas  engines  and  steam  turbines  was  likely 
to  be  of  more  immediate  practical  importance  than  the 
remote  possibility  that  the  mechanical  difficulties  connected 
with  the  gas  turbine  would  be  successfully  surmounted. 

Mr.  H.  M.  MARTIN  said  that  Professor  Burstall  had  men- 
tioned, in  connection  with  rotary  air  compressors,  0.4  as  the 
highest  efficiency  he  had  come  across.  In  a  turbine  compres- 
sor built  for  the  Farnley  Ironworks,  in  which  the  rotary  air 
compressor  was  driven  by  a  steam  turbine,  the  combined  effi- 
ciency as  determined  by  Professor  Goodman  was  61  per  cent. 
That  was  to  say,  the  "  air  horse-power  "  was  61  per  cent,  of  that 
theoretically  due  from  the  steam.  This  meant  that  the  effi- 
ciency of  the  compressor  per  se  was  something  like  80  per  cent. 

With  respect  to  experiments  on  divergent  nozzles,  it 
might  be  stated  that  some  had  been  made  by  Professor 
Stodola,  who  found  that  with  a  pressure  drop  of  from  10J 
to  YO  atmospheres,  the  loss  was  20  per  cent.  The  experiments 
were  not  entirely  satisfactory,  as  the  measurements  were 
made  by  means  of  a  small  tube  passing  centrally  down  the  noz- 
zle, which  acted  as  a  sort  of  Pitot  gauge.  In  fact,  Professor 
Stodola  concluded  that  in  the  absence  of  the  resistance  caused 
by  this  tube  the  loss  would  have  been  about  15  per  cent.* 

*  The  use  of  a  thermo-couple  would  seem  to  afford  a  means  of  measuring 
the  loss  in  a  divergent  nozzle  with  the  least  possible  disturbance  of  the  flow. 
With  such  an  instrument  the  distribution  of  temperature  throughout  the  nozzle 
could  be  determined,  and  this  known,  together  with  the  weight  discharged  per 
second,  the  efficiency  of  the  nozzle  could  be  readily  calculated  by  elementary 
thermodynamics. 


THE   GAS   TURBINE. 


89 


There  was  another  possibility  with  respect  to  gas  tur- 
bines which  he  did  not  know  whether  it  would  prove  prac- 
ticable to  work  out.  Consider  the  well-known  water  ejector, 
such  as  indicated  in  Fig.  34.  High-pressure  water  entering 
through  a  suitable-  nozzle  into  a  combining  cone  drew  in  and 


FIG.  34.— Water  ejector. 

carried  with  it  low-pressure  water  to  form  a  combined  jet. 
The  efficiency  claimed  for  the  appliance  was  over  90  per 
cent.  He  did  not  know  whether  it  would  be  possible  to  work 
an  air  ejector  on  the  same  lines.  The  method  would  be  to 
let  a  jet  of  products  of  combustion  at  high  pressure  develop 


FIG.  35.- 


Zero 
-Divergent  nozzle,  showing  varying  pressure. 


its  full  kinetic  energy  in  a  divergent  nozzle.  This  would  then 
be  utilized  to  draw  in,  say,  four  or  five  times  its  weight  of 
air  by  an  ejector,  and  the  combined  jet  having  a  correspond- 
ingly reduced  velocity  and  temperature  would  be  utilized 
to  drive  the  turbine.  Some  experiments  by  Professor  Stodola 
went  to  show  that  the  necessary  suction  could  be  obtained 


90  THE   GAS   TURBINE. 

with  an  air-jet.  Thus  he  found  that  if  a  divergent  nozzle 
designed  for  a  high  drop  of  pressure  was  used  for  a  smaller 
drop,  the  distribution  of  pressures  in  the  nozzle  was  such  as 
indicated  in  Fig.  35  (page  89).  Obviously,  if  holes  were 
put  through  the  walls  of  the  nozzle  in  the  region  of  low  pres- 
sure, air  would  be  drawn  in,  and  Professor  Stodola  had 
attempted  to  construct  an  ejector  somewhat  on  these  lines, 
but  so  far  had  failed  to  obtain  an  efficient  apparatus. 

Professor  ROBERT  H.  SMITH  said  that  much  useful  and 
interesting  information,  especially  upon  the  outflow  of  high- 
pressure  fluids  through  varying  shapes  of  nozzles,  was  to  be 
found  in  the  book  by  Professor  Stodola  on  "  Steam  Tur- 
bines."* As  the  author  in  his  Paper  referred  to  a  theory 
that  more  than  a  certain  critical  velocity  could  not  be  ob- 
tained in  such  nozzles,  he  might  mention  that  Professor 
Stodola's  experiments  showed  velocities  in  the  nozzles  which 
were  considerably  higher  than  the  critical  velocity  calcu- 
lated on  the  assumption  which  the  author  referred  to;  but 
when  the  critical  velocity  was  passed,  extremely  interesting 
phenomena  occurred,  which  had  been  suggested  by  the  dia- 
gram shown  by  Mr.  Martin,  Fig.  35  (page  89).  The  pres- 
sure oscillated,  not  in  time,  but  in  distance  along  the  axis  of 
the  nozzle.  Great  waves,  steady  waves,  of  pressure  existed. 
The  most  interesting  practical  point  resulting  from  these 
experiments  was  that  such  waves  of  pressure  did  not  serve 
any  useful  purpose,  and  that  the  nozzle  should  be  designed 
so  that  they  did  not  arise.  The  nozzle  could  be  designed 
for  each  discharge  pressure  so  that  the  waves  could  be 

*  "Die  Dampfturbinen,"  by  Dr.  A.  Stodola,  of  Zurich,  1903,  published  by 
J.  Springer.  Berlin.  See  pages  17-37.  English  translation  by  Dr.  L.  C.  Lowen- 
stein,  published  by  D.  van  Nostrand  Co.,  New  York,  and  Archibald  Constable 
&  Co.,  London. 

Other  recently  published  books  on  the  subject  are  "  Le  Turbine  a  Vapore 
et  a  Gaz,"  by  Ing.  Guiseppe  Belluzzo,  published  by  U.  Hoepli,  Milan,  1905; 
and  "Dampfturbinen,  Entwickelung,  Systeme,  Bau  u.  Verwendung,"  by  Wil- 
helm  Gentsch,  published  by  Williams  and  Norgate,  London,  1905. 


THE   GAS   TURBINE.  91 

smoothed  down  and  made  to  disappear.  That,  he  thought, 
was  the  most  useful  result  of  Professor  Stodola's  very  long 
and  exceedingly  interesting  series  ot  experiments  last  year. 

The  difficulty  to  which  Mr.  Atkinson  had  alluded  seemed 
to  be  the  greatest  difficulty  to  be  feared  in  gas  turbines, 
because  the  fluid  resulting  from  combustion  must  be  diluted 
very  greatly  in  order  to  keep  down  pressure  and  temperature 
within  practical  limits,  and  the  only  cheap  way  of  diluting 
it  was  with  an  excess  of  air.  There  would  be,  therefore,  a 
very  large  excess  of  extremely  hot  air  containing  large  quan- 
tities of  free  oxygen  passing  through  the  narrow  nozzles  and 
wheel  buckets,  and  he  fancied  these  would  be  rapidly  burned 
away.  He  was  surprised  to  hear  the  statement  that  air  com- 
pressing could  not  be  done  at  a  greater  efficiency  than  40 
per  cent.  He  knew  many  reciprocating  air  compressors  in 
which  it  was  possible  to  easily  attain  over  60  per  cent,  effi- 
ciency. Mr.  Henry  Davey  had  sketched  an  apparatus  he  had 
made  upon  a  small  scale,  Fig.  33  (page  80).  He,  Professor 
Smith,  had  spent  two  years  in  experimenting  upon  a  similar 
apparatus  on  a  larger  scale,  which  was  designed  for  600 
pounds  working  pressure  and  45  indicated  horse-power,  and 
he  had  worked  it  at  130  pounds;  but  it  was  not  for  the  com- 
bustion of  gas,  but  for  that  of  oil.  The  difficulty  had  been, 
so  far,  one  similar  to  that  which  Mr.  Davey  referred  to, 
namely,  the  occasional  sudden  extinction  of  the  flame  and  the 
difficulty  of  controlling  the  flame,  leading,  in  his  apparatus, 
to  an  inconvenient  rush  of  the  water  over  into  the  fire-tubes. 

In  the  Paper  there  was  a  very  interesting  and  important 
remark  (page  29)  relating  to  Carnot's  formula  for  the 
efficiency  of  an  ideal  heat  engine.  This  formula  was  not 
intended  for  practical  application  to  working  plant,  but  was 
framed  only  for  the  purpose  of  proving  a  theoretical  prop- 
osition, a  proposition  of  immense  value  in  the  science  of 
thermodynamics.  It  was  not  a  measure  of  efficiency  appli- 
cable to  any  heat  engine  which  it  was  possible  to  construct 
and  work.  The  upper  and  lower  limits  of  temperature  might 


92  THE   GAS   TURBINE. 


be  greatly  changed  without  to  any  extent  changing  the  ther- 
modynamic  efficiency.  It  was  an  historical  fact  that  every 
engine  that  had  been  made  and  worked  successfully  had  cut 
down  its  upper  temperature  limit  before  it  had  obtained 
practical  success. 

He  was  struck  by  the  remark  (page  76)  that  "With  the 
average  user  of  a  small  engine,  producing,  say,  100  B.H.P.- 
hours  per  week,  a  reduction  of  £10  in  the  initial  cost  is  of 
more  consequence  than  a  reduction  of  2  cubic  feet  per  B.H.P.- 
hour  in  gas  consumption."  It  occurred  to  him  that  that 
was  rather  an  extravagant  estimate  of  the  value  of  low 
initial  cost.  It  was  usually  his  fate  to  argue  in  favor  of 
greater  consideration  of  initial  cost.  Considering  that  2 
cubic  feet  per  B.H.P.  at  100  B.H.P.-hours  per  week  was 
200  cubic  feet  of  gas  per  week,  and  taking  gas  at  2s.  6d.  per 
thousand,  that  meant  26s.  a  year;  26s.  was  13  per  cent,  upon 
£10,  and  13  per  cent,  was  rather  a  high  percentage  to  take 
in  the  comparison.  Perhaps  a  saving  of  3  cubic  feet  of  gas 
per  B.H.P. -hour  in  an  engine  of  this  small  size  working 
with  so  bad  a  load  factor  might  be  more  fairly  comparable 
with  the  advantage  of  £10  decrease  in  capital  cost.  On 
page  76  the  author  suggested  the  use  of  gas  turbines  upon 
motors  for  certain  reasons  which  he  gave,  but  surely  the 
difficulty  of  using  any  sort  of  gas  engine  on  the  motor  was 
not  in  the  engine  itself  but  in  the  weight  and  bulk  of  the 
vessels  that  had  to  be  carried  to  hold  the  gas.  Some  years 
ago  he  worked  that  out,  and  he  found  it  was  practically 
impossible,  even  with  the  high  pressures  that  were  used  in 
weldless  steel  gas  cylinders,  to  carry  any  reasonable  bulk  of 
gas  in  a  motor  car.  Lower  down  on  the  same  page  the  author 
made  a  very  useful  remark,  pointing  out  that  in  order  to  dis- 
place electric  driving  the  turbine  would  only  require  to  possess 
an  efficiency  greater  than  the  efficiency  of  the  central  station 
engine  multiplied  by  the  efficiencies  of  dynamo,  mains,  and 
motor.  If  those  four  efficiencies  were  multiplied  together  a 
very  low  compound  efficiency  would  be  obtained  in  the  end. 


THE   GAS   TURBINE.  93 

Mr.  NEILSON,  in  reply  to  the  discussion,  stated  that  Pro- 
fessor Bin-stall's  remarks  on  rotary  compressors  and  their 
efficiencies  had  been  already  replied  to  by  Mr.  Martin  (page 
88).  It  by  no  means  followed  that  an  efficient  rotary  com- 
pressor could  not  be  used,  although  the  turbine  compressors 
were  not  successful  at  high  pressures.  Turbine  compressors 
had  been  used  up  to  about  80  pounds  pressure  or  so,  that 
was,  compressors  arranged  like  a  converse  steam  turbine. 
It  was  quite  reasonable  to  suppose  that  such  compressors 
would  not  be  efficient  at  high  pressures,  as  they  had  a  great 
number  of  stages,  and  the  air  was  somewhat  roughly  handled 
at  each  stage.  He  thought  there  was  great  room  for  inves- 
tigation in  the  matter  of  trying  to  find  an  efficient  rotary 
compressor  on  another  principle.  Professor  Burstall  had 
stated  that  a  gaseous  charge  could  not  be  allowed  to  remain 
in  contact  with  the  metal  for  long  without  a  great  transfer- 
ence of  heat,  and  that  gas  was  very  different  from  steam  in 
that  respect.  In  steam  turbines  with  superheated  steam 
there  was  practically  a  gas  at  the  high  pressure  end  of  the 
turbine.  Superheating  had  very  much  improved  the  effici- 
ency of  steam  turbines,  and  it  would  be  reasonable  to  sup- 
pose that  no  great  loss  of  heat  occurred  at  the  high  pressure 
end  of  the  turbine.  He  believed  experiments  had  been  made 
at  the  Manchester  Technical  School  with  a  Parsons  turbine, 
and  the  temperatures  taken  at  different  stages  of  the  expan- 
sion, but  he  had  not  seen  the  figures.  Those  experiments 
were  with  steam  slightly  superheated.* 

Professor  Burstall  had  referred  to  the  possibility  of  get- 
ting a  material  some  day  that  would  stand  the  high  stresses 
caused  by  high  speeds.  During  the  last  few  years  there  had 
been  very  great  improvement  in  that  respect.  He  did  not 
think  that  a  De  Laval  turbine,  such  as  the  300-H.P.  now 

*  The  author  subsequently  saw  the  figures  through  the  courtesy  of  Mr. 
Mellanby;  but  the  superheat  was  so  slight  that  he  considered  the  figures, 
although  interesting,  were  of  no  value  in  the  present  instance. 


94  THE   GAS   TURBINE. 

built,  could  have  been  built  20  years  ago,  as  there  was  no 
material  then  to  stand  the  enormous  stresses.  It  had  to 
be  remembered  that  the  stresses  varied  pretty  nearly  as  the 
square  of  the  velocity,  so  that,  if  the  velocity  was  doubled 
there  was  four  times  the  stress.  The  experiments  mentioned 
at  the  end  of  the  Paper  certainly  would  cost  a  great  deal  of 
money.  Those  with  divergent  nozzles  would  perhaps  entail 
least  expense,  as  such  experiments  would  not  require  a  great 
amount  of  apparatus.  Professor  Stodola's  experiments  were 
exceedingly  interesting,  but  it  was  impossible  to  take  the 
results  as  being  very  exact.  Professor  Stodola  admitted 
that  his  measuring  apparatus  was  of  such  a  nature  as  would 
be  apt  to  distort  the  results.  For  example,  in  his  nozzle  he 
had  a  measuring  tube  which  was  very  small,  but  still  of  a 
diameter  that  was  appreciable  considering  the  minimum 
diameter  of  the  nozzle.  Experiments  on  the  effect  of  wind 
pressure  on  different  bodies  had  been  made  and  they  were 
described  before  the  Institution  of  Civil  Engineers*  by  Dr. 
T.  E.  Stanton.  The  experimenters  discovered  that  in  order 
to  get  reliable  results  the  models  they  put  in  the  air  duct  had 
to  be  very  small  compared  with  the  dimensions  of  the  duct. 
That  was  with  a  comparatively  small  velocity  of  air.  In  Pro- 
fessor Stodola's  experiments  the  velocity  of  the  fluid  was  enor- 
mous, and  the  effect  of  any  body  in  the  centre  of  the  jet  would 
presumably  make  a  much  greater  difference.  Therefore,  while 
Professor  Stodola's  experiments  were  interesting,  further 
investigations  were  required  in  connection  with  the  matter. 
With  regard  to  the  fluctuation  of  pressure  mentioned  by 
Mr.  Martin  and  Professor  Smith  as  being  found  by  Professor 
Stodola,  the  steam  in  passing  through  certain  nozzles  fell  in 
pressure  more  than  it  should  do,  and  then  fluctuated  up  and 
down  in  regular  beats  before  it  remained  steady  at  the  final 
pressure.  Fig.  36  illustrated  the  oscillations  of  pressure, 
which  were  like  those  of  a  spring.  In  the  diagram,  heights 

*  Proceedings  Institution  of  Civil  Engineers,  1903,  Vol.  clvi,  page  78. 


THE   GAS   TURBINE. 


95 


represented  pressure,  and  horizontal  distances  represented 
measurements  along  the  nozzle.  He  did  not  think  Professor 
Stodola  was  the  first  to  discover  that.  It  illustrated  what 
he  had  said  earlier,  that  it  was  very  difficult  in  many  cases 
to  tell  to  whom  credit  was  due.  The  fact  was  mentioned  in 
a  Paper*  which  Mr.  Hodgkinson  read  in  America  some  few 
years  ago,  but  even  he  did  not  seem  to  be  the  first  to  discover 
the  phenomenon. 


Measurements 
a.?or?g  nozzfe 

FIG.  36. — Fluctuating  pressure  of  steam  passing  through  nozzle. 

Mr.  Atkinson  had  referred  to  the  statement  about  super- 
heating (page  30).  Of  course,  superheating  did  increase 
the  efficiency,  not  owing  to  thermodynamic  reasons,  but  be- 
cause of  the  reduction  in  friction  and  for  other  reasons  which 
he  need  not  go  further  into.  Mr.  Martin  alluded  to  the  pro- 
posal to  draw  in  an  extra  quantity  of  air  to  mix  with  the 
products  of  combustion  in  order  to  cool  down  the  tempera- 
ture of  the  explosion  and  get  a  more  reasonable  temperature, 
and  he  mentioned  the  proportion  as  4  pounds  of  air  to  1 
pound  of  products  of  combustion.  The  lower  temperature 
suited  the  turbine,  but  it  had  to  be  remembered  that  in  a 
practical  turbine  the  extraction  of  the  available  energy  of  the 

*  Proceedings,  Engineers'  Society  of  Western  Pennsylvania,  Nov.,  1900. 


96  THE   GAS   TURBINE. 

fluid  was  never  complete,  and  that  with  this  air-dilution 
scheme,  instead  of  discharging  1  pound  of  fluid  with  a  certain 
amount  of  unrecovered  energy,  it  would  be  necessary  to  dis- 
charge 5  pounds,  thus  throwing  away  five  times  the  available 
energy  that  would  be  otherwise  thrown  away.  If  water 
instead  of  air  were  used  to  dilute  the  products  of  combus- 
tion, the  mass  of  fluid  would  not  be  increased  to  the  same 
extent.  A  somewhat  similar  proposal  had  been  made  as 
regards  steam  turbines,  namely,  to  dilute  the  steam  from  a 
divergent  nozzle  with  water  or  other  fluid  in  order  to  bring 
down  the  velocity  so  as  to  enable  the  velocity  to  be  utilized 
conveniently  in  the  turbine  wheel.  This  would  allow  the 
wheel  to  run  at  a  lower  speed.  Instead,  however,  of  dis- 
charging 1  pound  of  fluid  with  a  certain  final  velocity,  the 
scheme  would  involve  the  discharging  of,  say,  5  pounds  or 
6  pounds. 

Professor  Smith  had  referred  to  the  question  of  the  rela- 
tive advantage  of  low  initial  cost  and  low  working  expenses 
(page  92).  The  case  mentioned  by  Professor  Smith  he  had 
worked  out,  but  he  forgot  what  the  saving  amounted  to  as  a 
percentage  of  the  extra  capital.  Taking  it  as  13  per  cent. 
(as  given  by  Professor  Smith),  he  thought  that  with  a  small 
turbine  the  reduction  in  initial  cost  would  be  of  more  im- 
portance than  the  13  per  cent,  saving.  It  was  not  like  put- 
ting money  into  a  building.  No  one  could  say  how  long  the 
engine  was  going  to  be  up-to-date,  and  no  one  knew  how 
long  it  would  be  before  another  engine  was  required.  More- 
over, small  users  generally  wanted  money  at  the  time.  He 
thanked  the  Institution  for  the  vote  of  thanks  that  had  been 
accorded  to  him. 

Communications. 

Mr.  EDWARD  BUTLER  wrote  that  perhaps  the  greatest 
obstacle  in  the  way  of  the  production  of  an  efficient  gas  tur- 
bine— namely,  "the  very  low  reactionary  value  and  destruc- 


THE   GAS   TURBINE.  97 

tive  property  of  a  highly  heated  gas,  as  compared  with  steam 
of  the  same  pressure" — could  be  removed  by  a  combination 
of  apparatus  in  which  gas  and  air  would  be  supplied  to  a 
mixing  chamber  communicating  with  a  series  of  long  explo- 
sion chambers  with  siphon  formations  for  receiving  water. 
The  modus  operandi  being  for  the  series  of  explosion  cham- 
bers to  be  charged  with  explosive  mixture  and  fired  in  rota- 
tion, the  effect  of  the  explosions  would  force  out  the  water 
contained  in  the  well  or  siphon  formation  of  each  tube  in  suc- 
cession and  this  water  could  be  directed  on  to  the  wheel  of  a 
water  turbine.  Succeeding  charges  of  gas  mixture  would 
enter  automatically  from  the  mixing  chamber  through  non- 
return valves  immediately  after  each  explosion.  The  only 
operating  mechanism  required  would  be  means  for  quickly 
filling  the  siphons  with  water  and  for  igniting  the  mixture 
in  the  series  of  five  or  six  explosion  tubes,  by  which  an  almost 
continuous  stream  of  water  would  be  directed  onto  the  tur- 
bine wheel  at  high  velocity,  thus  avoiding  all  the  trouble 
that  would  follow  from  any  method  of  employing  a  turbine 
wheel  actuated  direct  by  the  hot  rarefied  gases  of  combus- 
tion. He  offered  this  solution  of  a  gas  power  turbine,  after 
having  had  some  experience  in  the  working  of  a  steam  tur- 
bine worked  somewhat  on  these  lines,  namely,  with  water 
accelerated  by  a  steam  injector  and  boiler. 

Mr.  DUGALD  CLERK  wrote  that  he  had  read  the  Paper 
with  much  interest,  and  he  quite  sympathized  with  the 
author  in  his  effort  to  clear  up  in  a  preliminary  way  the  many 
abstract  points  which  required  consideration  before  the 
practical  problem  of  the  gas  turbine  could  be  attacked  with 
any  chance  of  success.  In  view  of  the  wonderful  results 
obtained  by  the  Hon.  C.  A.  Parsons  and  his  imitators  with 
the  steam  turbine,  it  was  very  natural  that  the  attention 
of  engineers  should  be  called  to  the  problem  of  the  gas  tur- 
bine. Belonging  to  the  older  school  of  engineer  inventors 
and  having  become  somewhat  mentally  fatigued  by  the 
7 


98  THE   GAS   TURBINE. 

numerous  difficulties  experienced  with  cylinder  and  piston 
gas  engines  in  every  stage  of  their  progress,  it  might  be  that 
the  writer  was  less  likely  to  take  a  hopeful  view  of  the  gas 
turbine  problem  than  a  younger  engineer,  whose  life  and 
practical  engineering  difficulties  were  still  before  him. 
Whether  this  were  so  or  not,  he  must  confess  that  his  view 
of  the  future  of  the  gas  turbine  was  not  so  hopeful  as  the 
author's.  The  difficulties  appeared  to  be  even  greater  than 
the  author  had  apprehended.  Mr.  Neilson  rightly  laid  a 
certain  stress  on  the  relatively  low  efficiencies  possible  in  tur- 
bine compressing  plants;  but  he  did  not  think  he  had  laid 
sufficient  stress  upon  the  similarly  low  efficiency  of  expan- 
sion in  steam  turbines  of  existing  types.  No  doubt  the 
author  had  clearly  in  his  mind  the  fact  that  there  were  spe- 
cial advantages  in  the  steam  turbine  which  counterbalanced 
the  disadvantages  of  relatively  inefficient  expansion.  The 
steam  turbine  had,  to  begin  with,  the  great  advantage  of 
practical  freedom  from  losses  due  to  initial  condensation. 
It  had  the  further  great  advantage  of  expansion  to  a  much 
lower  pressure  point  than  could  ever  be  effectively  attained 
with  a  reciprocating  steam  engine.  These  two  advantages, 
in  the  case  of  steam,  undoubtedly  enabled  the  Parsons  tur- 
bine to  reach  figures  of  economical  steam  consumption  which 
were  not  touched  at  all  by  ordinary  reciprocating  steam 
engines,  and  were  very  rarely  reached  even  in  special  recip- 
rocating steam  engines  using  high  superheats.  These  ad- 
vantages of  no  initial  condensation  and  largely  extended 
expansion  were  advantages  special  to  steam;  they  were  not 
advantages  which  would  be  found  in  using  a  turbine  con- 
struction even  for  the  purpose  of  expanding  high  pressure 
cool  gases,  such  as  compressed  atmospheric  air.  In  an  ordi- 
nary gas  engine  cylinder,  the  efficiency  of  compression  and 
expansion  of  the  gaseous  contents  of  the  cylinder  (without 
combustion  at  all)  was  so  high  that  practically  no  difference 
could  be  detected  between  the  compression  and  expansion 


THE   GAS   TURBINE. 99 

lines  of  the  air  within  the  cylinder  during  successive  com- 
pression and  expansion  strokes.  Practically,  what  one  might 
call  the  efficiency  of  gaseous  compression  and  expansion  in 
an  ordinary  gas  engine  cylinder  was  certainly  not  less  than 
99  per  cent.  This,  undoubtedly,  enabled  engines  to  be  oper- 
ated economically  with  large  proportionate  values  of  nega- 
tive work.  If,  however,  the  efficiency  of  compression  had 
been,  say,  70  per  cent. — a  figure  higher  than  any  turbine  air- 
compressor  could  give  at  present — and  the  efficiency  of  ex- 
pansion 80  per  cent. — a  figure  higher  than  any  existing  tur- 
bine could  give  operated  by  expanded  compressed  air — even 
then  the  united  efficiencies  would  only  amount  to  56  per 
cent.  That  is,  assuming  the  gases  to  be  heated  for  the  ex- 
pansion period,  the  loss  to  be  made  good  to  bring  the  dia- 
gram up  to  unity  would  be  44  per  cent. ;  that  is,  if  the  volume 
of  the  gas  were  increased  by  heating  from  56  to  100,  then  the 
expansion  would  only  be  sufficient  to  produce  a  diagram 
which  would  keep  the  engine  running  if  it  were  quite  friction- 
less.  In  the  writer's  view,  therefore,  the  problem  to  be  faced 
required  not  only  the  invention  of  a  turbine  air  compressor 
compressing,  say,  to  200  pounds  per  square  inch,  with  an 
efficiency  of  something  nearly  90  per  cent.,  but  it  also  re- 
quired the  invention  of  a  turbine  motor  engine  which  would 
give  a  like  efficiency  of  expansion  of  the  gases  so  compressed. 
High  efficiencies  of  compression  and  expansion  of  gases,  such 
as  air,  were  undoubtedly  theoretically  possible;  but  he  knew 
of  no  turbine  yet  in  existence  which  would  give  any  efficien- 
cies such  as  he  had  indicated.  Until  these  efficiencies  were 
obtained,  it  seemed  to  the  writer  impossible  to  design  any 
gas  turbine  having  a  chance  of  success. 

The  author  had  very  accurately  made  clear  the  point 
that,  in  some  types  of  turbine,  low  temperature,  and  there- 
fore large  negative  work,  was  necessary  for  working  condi- 
tions. He  himself  could  not  help  thinking  that,  although 
the  high  temperatures  he  proposed— 2000°  C.  (3632°  F.) 


100  THE   GAS  TURBINE. 

and  so  forth — certainly  diminished  negative  work,  they  yet 
introduced  for  the  inventor  a  much  worse  condition  from 
the  points  of  view  of  durability  of  blades,  and  heat  losses  if 
the  blades  were  kept  cool.  There  seemed  to  be  no  possibility 
whatever  of  working  a  turbine  at  temperatures  approaching 
2000°  C.  The  De  Laval  type  was  proposed  by  the  author 
to  enable  temperatures  to  be  reduced  while  the  energy  was 
maintained  in  the  shape  of  velocity  of  the  moving  gases. 
He  could  not  help  thinking  that  any  scheme  which  allowed 
of  such  reduction  would  also  cool  the  expanding  gases  by  the 
very  conditions  required  in  the  constructions  of  the  expand- 
ing nozzle.  He  did  not  see  any  immediate  future  for  a  gas 
turbine,  except  in  possibly  utilizing  the  exhaust  gases  from 
reciprocating  engines,  which  at  present  were  liberated  under 
considerable  pressures.  He  feared  that  the  attack  of  the 
problem  of  an  efficient  turbine  air  expander  was  more 
within  the  province  of  the  practical  inventor  than  the  scien- 
tific investigator.  He  would  be  much  interested  to  hear 
any  ideas  Mr.  Neilson  might  have  in  the  direction  of  pro- 
ducing efficient  turbine  compressors  and  expanders. 

He  hoped  that  the  author  would  not  be  discouraged  at 
the  somewhat  pessimistic  tone  of  these  remarks.  He  had 
often  thought  over  this  subject,  and  had  not  as  yet  seen  any 
hope  of  getting  as  good  results,  either  as  to  economy  or  dura- 
bility, with  gas  turbines  as  were  obtained  with  reciprocating 
engines. 

Mr.  W.  J.  A.  LONDON  wrote  that,  in  studying  the' Paper, 
one  could  not  help  feeling  impressed  by  the  thoroughness 
with  which  the  author  had  dealt  with  the  various  possible 
cycles  to  which  engineers  were  to  look  in  the  future  gas  tur- 
bine. The  most  interesting  point,  however,  in  the  writer's 
opinion,  was  the  way  in  which  the  author's  investigations 
showed  the  difficulties  to  be  met  with  in  the  successful  de- 
signing of  such  machines.  It  was  a  pity  that  he  had  not 


THE   GAS  TURBINE/  ; 


attempted  to  consider  from  a  more  practical  standpoint 
several  of  the  cycles  set  forth;  had  he  done  this,  the  writer 
could  not  help  feeling  confident  that  he  would  have  omitted 
several  of  the  cycles  referred  to. 

On  page  32  a  reference  was  made  to  a  combustion 
chamber  where  the  burning  gases  could  rest  before  entering 
the  turbine.  He  thought  this  would  be  a  great  source  of 
loss,  because  this  chamber  would  have  to  be  cooled,  and,  to 
allow  the  gases  to  remain  in  a  chamber  with  cooled  walls,  a 
great  amount  of  efficiency  would  naturally  be  lost.  Further, 
on  the  same  page,  the  author  referred  to  a  mixture  of  air 
and  fuel  being  always  supplied  to  the  flame  with  a  velocity 
greater  than  that  of  the  propagation  of  the  flame.  This,  in 
the  writer's  opinion,  would  be  a  very  difficult  thing  to  do, 
especially  at  the  high  outgoing  velocities  attending  the  ex- 
panding gas.  On  page  39  the  author  referred  to  the  Par- 
sons turbine  with  steel  blades  for  working  at  about  700°  C. 
(1292°  F.).  This  temperature  was  very  high,  and  it  was 
doubtful  whether  any  blades  with  sharp  edges  could  be 
made  to  withstand  it  for  any  length  of  time. 

In  Cycle  I,  Case  2  (page  39),  the  author  proposed  to 
circulate  water  in  the  revolving  part.  If  he  would  consider 
the  difficulties  to  be  met  with  in  circulating  water  in  the 
revolving  chamber,  the  writer  thought  he  would  find  that  it 
would  be  a  more  difficult  problem  than  he  considered.  The 
water  would  be  thrown  against  the  outer  walls,  which  was 
the  point  to  be  desired,  but  whether  the  circulation  could  be 
arranged  without  seriously  interfering  with  the  running  bal- 
ance of  the  machine  was  another  question.  Further,  even 
if  the  rotating  drum  were  cool,  this  would  not  effectively  cool 
the  blades,  and  to  do  this  as  the  author  suggested,  by  making 
the  blades  hollow,  would  require  very  large  blades  with 
internal  pipe  arrangements  for  ensuring  circulation.  With 
his  device  he  claimed  that  2000°  C.  was  allowable;  this  cor- 
responded to  3632°  F.,  or  above  the  melting-point  of  steel, 


KJ2  1THE   GAS  TURBINE. 

so  that  it  was  hardly  likely  that  any  sharp  edges  could  be 
expected  to  remain  on  the  blades.  For  mechanical  reasons 
he  did  not  think  one  should  look  for  the  gas  turbine  on  the 
Parsons  principle,  but  more  on  the  lines  of  the  De  Laval,  as 
set  forth  in  Cycle  I,  Case  3a  (page  48),  where  the  gas  was 
expanded  in  nozzles,  and  the  temperature  reduced  before 
the  working  fluid  came  into  contact  with  the  moving  blades. 

The  author  referred  (page  56)  to  a  combination  of 
reciprocating  engines  and  turbines  working  with  gas  on  the 
principle  now  being  adopted  in  connection  with  steam 
engines  and  turbines.  It  would  be  interesting  to  learn  what 
gain  this  system  had  over  reciprocating  engines.  The  idea 
in  the  steam  combined  system  was  that  the  reciprocating 
engines  were  perhaps  more  economical  at  lower  speeds  than 
the  normal.  The  steam  turbine  working  non-condensing 
had  great  difficulty  in  competing  with  the  reciprocating 
engine,  but  when  working  condensing  the  conditions  were 
different,  and  the  turbine  was  more  capable  of  taking  care 
of  what  might  be  called  the  tail  end  of  the  expansion  curve. 
These  conditions  when  working  condensing  did  not  come 
into  account  when  working  non-condensing,  as  in  the  case 
of  a  gas  turbine,  so  that  it  was  doubtful  whether  the  com- 
bined system  would  be  even  as  economical  as  a  gas  engine  of 
the  ordinary  reciprocating  type. 

The  system  which  the  writer  thought  offered  the  greatest 
possibilities  was  on  the  principle  of  Cycle  III,  Case  1  (page 
59),  where  the  steam  jet  was  inserted  into  the  gas,  thus 
utilizing  the  expansion  of  the  superheated  steam  and  reduc- 
ing the  temperature  of  the  working  fluid  to  within  practical 
limits.  The  ideal  efficiency  of  0.33  and  the  ratio  of  negative 
work  of  gross  work  of  0.41  did  not  look  as  satisfactory  as 
some  of  the  other  cases  set  forth,  but  it  was  undoubtedly 
more  practical,  and  it  seemed  more  than  likely  that  the  solu- 
tion of  the  difficulty  would  be  found  in  this  direction.  Re- 
ferring to  the  author's  remarks  (page  69)  on  the  velocity 


THE   GAS   TURBINE.  103 

of  gases  issuing  from  diverging  nozzles,  there  must  be  a 
limiting  velocity  for  the  flow  of  gas  through  an  orifice,  this 
velocity  being  at  a  point  where  the  weight  discharged  multi- 
plied by  the  velocity  due  to  difference  in  pressure  was  a 
maximum.  He  thought  this  point  had  been  experimentally 
investigated,  and  it  had  been  found  that  the  point  of  maxi- 
mum discharge  was  when  the  ratio  of  internal  to  external 
pressure  varied  between  0.5  and  0.6  according  to  the  nature 
of  the  gas.  This  pressure  of  0.5  to  0.6  initial  pressure  would 
be  at  the  throat,  or,  in  other  words,  at  the  smallest  part  of 
the  nozzle,  and  the  velocity  had  been  found  to  be  somewhere 
about  1500  feet  per  second.  However  much  the  difference 
of  pressure  was  increased,  this  law  remained  good,  and  no 
more  gas  would  pass  through  the  orifice,  nor  would  the 
velocity  at  the  throat  increase.  The  terminal  velocity,  how- 
ever, would  be  greater  in  proportion  to  the  drop  in  pressure. 

Mr.  E.  KILBURN  SCOTT  wrote  that  he  thought  the  author 
struck  the  keynote  of  the  present  position  when  he  suggested 
(page  78)  that  a  thorough  set  of  experiments  should  be 
made  and  the  results  published.  The  information  so  ob- 
tained by  the  engineering  world  would  be  extremely  valu- 
able, whatever  the  price,  as  it  would  save  much  time  and 
overlapping  if  the  several  fundamental  considerations  in- 
volved could  be  investigated  straight  away.  It  was  essen- 
tially a  matter  for  some  public  body,  and  he  suggested  that 
the  Institution  of  Mechanical  Engineers  should  undertake 
the  work.  The  tendency  of  the  times  was  well  shown  by  the 
working  arrangement  between  the  General  Electric  Co.  of 
America  and  the  Allgemeine  Elektricitats  Gesellschaft  of 
Berlin,  whereby  experimental  data,  drawings,  etc.,  were  now 
the  common  property  of  both  firms.  This  arrangement  was 
come  to  with  the  idea  of  cutting  down  expenses,  and  at  the 
same  time  facilitating  the  progress  of  experimental  research 
and  of  new  designs. 


104 


THE   GAS  TURBINE. 


The  high  temperatures  and  high  velocities  involved  in 
working  turbines  with  gas,  and  the  fact  that  the  hot  gases 
came  so  intimately  into  contact  with  the  metal  parts,  called 
for  an  investigation  as  to  the  most  suitable  metal  to  employ. 

Separate  blades,  caulked  in  as  with  the  Parsons  turbine, 
would  hardly  do  for  gas  turbines,  as  this  construction  was  not 
even  satisfactory  at  the  temperature  of  highly  superheated 

PRINCIPLES    OF   TWO    GERMAN   ARRANGEMENTS   OF   TURBINES. 

ft 


1     I     I 

<Steam  or  Ga*s. 
FIG.  37. — Principle  of  Bucholz  turbine. 

This  <Sfej/7t  or  G<ss 
space  gr<3dua//y 
contracts 


FIG.  38.— Principle  of  Patschke  turbine. 

steam.  New  turbines  were,  however,  coming  forward 
which  had  not  so  delicate  a  constitution.  The  Buchol/,* 
for  example  (Fig.  37)  had  a  series  of  metal  discs  with 
holes  drilled  through  them  at  an  angle,  and  against  which 
the  working  medium  impinged;  and  the  ingenious  Patschke 
turbine  (Fig.  38)  had  the  rotating  part  simply  in  the  form  of 
a  drum  with  a  number  of  holes  drilled  in  the  rim.  With  such 

*  "Electrical  Review,"  January  8th,  1904,  page  66. 


THE   GAS   TURBINE.  105 

solid  construction,  exceedingly  high  velocities  could  be  at- 
tained, and  temperature  had  very  little  effect,  whilst  these 
two  designs  had  the  further  advantage  of  being  reversible. 

The  question  of  water-supply  to  the  heated  metal  was 
mainly  a  matter  of  mechanical  design,  and  he  thought  it  was 
less  difficult  to  arrange  water-circulation  in  the  interior  of  the 
rotating  part  of  a  turbine  than  it  was  to  get  it  into  the  pistons 
and  exhaust  valves  of  a  large  slow-running  power  gas  engine. 

In  comparing  gas  turbine  with  electric  motor  driving,  it 
must  be  remembered  that  practically  all  turbines  ran  at 
speeds  which  were  unsuitable  for  driving  shafting  and  ma- 
chine tools,  and  that  the  latter  were  par  excellence  the  very 
things  for  which  the  electric  motor  was  most  suitable,  by 
reason  of  the  ease  with  which  the  motor  could  be  started 
and  stopped  or  its  speed  varied,  and  also  moved  about  for 
use  with  portable  tools.  A  pipe  containing  gas  could  never 
compete  with  an  electric  cable  for  such  work.  As  a  matter 
of  fact,  the  author  need  not  worry  as  to  uses  for  gas  tur- 
bines; only  let  it  be  clearly  demonstrated  that  they  were 
commercial,  and  they  would  become  the  favorite  prime- 
mover  for  driving  electric  generators,  and  in  that  direction 
alone  there  was  scope  enough.  Any  one  prophesying  two 
years  ago  that  the  Curtis  turbine  would  attain  its  present 
position  in  the  United  States  would  have  been  thought  a 
dreamer,  yet  the  writer  had  recently  seen  five  stations 
equipped  with  8000  horse-power  Curtis  sets  running  with- 
out a  hitch.  So  far  as  power  station  work  in  the  United 
States  was  concerned,  steam  turbines  were  preferred  to 
reciprocating  steam  engines,  and  he  believed  that  one  day 
gas  turbines  would  come  to  the  front  just  as  rapidly. 

Mr.  GEORGE  A.  WIGLEY  wrote  that  he  thought  it  was 
remarkable  that  during  the  discussion  no  direct  reference 
was  made  to  oil  turbines  or  engines,  with  the  exception  of  a 
few  remarks  on  the  Diesel  engine.  One  of  the  first  problems 


106  THE   GAS   TURBINE. 

to  be  considered  with  regard  to  a  gas  turbine  was  the  pro- 
duction of  the  gas,  and  if  it  were  necessary  to  supply  a  gas- 
producer  even  of  the  modern  suction  type,  a  pump  for  com- 
pressing this  gas  and  a  mixing  chamber,  it  was  useless  to 
compare  such  a  plant  with  an  electric  motor,  irrespective  of 
maintenance  costs,  but  if  a  mineral  oil  were  substituted  for 
the  gas  the  problem  immediately  assumed  a  different  aspect. 
In  Cycle  III,  Case  2  (page  61),  the  author  clearly 
pointed  out  the  advantages  to  be  obtained  by  the  use  of 
water  or  steam  with  the  gas,  and  this  would,  of  course,  hold 
good  with  oil  as  fuel,  the  ratio  of  negative  work  to  gross  work 
being  decreased,  but  it  was  this  question  of  negative  work 
which,  in  the  writer's  opinion,  was  most  important.  In  oil 
(mineral  oil)  they  had  what  was  practically  a  gas  compressed 
to  liquefaction  all  ready  to  hand  in  a  very  convenient  form, 
and  in  such  a  condition  that,  when  intimately  mixed  with  the 
proper  amount  of  oxygen,  it  formed  a  gas  which  was  ready 
to  give  up  a  great  proportion  of  the  work  which  would  be  or 
had  been  necessary  to  compress  it  to  liquefaction.  So  that 
they  had  what  was  to  all  intents  and  purposes  a  gas  already 
compressed;  and  as  this  gas  had  had  work  done  upon  it  far 
greater  in  amount  than  was  necessary  for  the  required  im- 
mediate object,  it  followed  that  the  oil,  when  fired,  gave  up 
this  work,  and  not  only  reduced  the  negative  work  given  out 
by  the  turbine  to  the  extent  of  that  required  to  compress 
the  gas  to  the  necessary  pressure,  but  also  reduced  the  excess 
work  required  to  liquefy  it,  less  that  corresponding  to  the 
latent  heat  of  vaporization.  The  result  was  that  the  nega- 
tive work  calculated  for  gas  was  greatly  reduced  if  oil  were 
used,  the  extra  work  being  given  in  the  convenient  form  of 
heat  and  kinetic  energy  of  the  particles. 

Mr.  NEILSON,  in  reply  to  the  written  communications, 
wrote  that  Mr.  London  had  raised  the  question  as  to  whether 
if  the  burning  gases  were  allowed  to  rest  a  short  interval  in  a 


THE   GAS   TURBINE.  107 

combustion  chamber  before  being  taken  to  the  turbine,  there 
would  not  be  a  great  loss  of  heat.  He  (the  author)  agreed 
that  this  question  deserved  consideration,  but  he  did  not 
think  that  there  need  be  anything  like  as  great  a  loss  of  heat 
to  the  walls  of  this  combustion  chamber  as  to  the  walls  of  the 
combustion  chamber  of  a  reciprocating  engine,  which  re- 
quired to  be  kept  much  cooler  than  would  be  necessary  in 
the  case  of  a  turbine.  As  regards  the  last  remarks  made  by 
Mr.  London,  it  must  be  noted  that  the  highest  velocity  ob- 
tainable when  a  gas  issued  from  a  simple  orifice  was  not 
necessarily  the  highest  velocity  that  could  be  obtained 
when  a  divergent  nozzle  was  placed  on  the  delivery  side  of 
the  orifice. 

With  regard  to  supplying  the  air  and  gas  at  a  velocity 
higher  than  the  velocity  of  the  propagation  of  the  flame, 
mentioned  by  Mr.  London,  he  did  not  think  that  this  was 
really  a  difficult  problem  with  the  gas  turbine.  With  a  re- 
ciprocating engine  it  was  complicated,  but  with  a  gas  tur- 
bine having  a  continuous  flow  of  gas  it  should  not  be  difficult. 
With  a  mixture  of  a  given  gas  and  air  in  constant  propor- 
tion, the  flame  would  have  a  given  rate  of  propagation;  and, 
if  care  were  taken  to  supply  the  air  and  gas  to  the  combustion 
chamber  at  a  greater  velocity,  there  should  be  no  firing  back. 
Mr.  London  had  referred  to  the  proposal  to  circulate  water 
in  the  turbine.  It  was  said  in  the  Paper  that  this  had  been 
proposed,  but  he  (the  author)  did  not  propose  it  himself, 
and  he  had  not  much  faith  in  it. 

He  agreed  with  Mr.  Kilburn  Scott  as  to  the  benefit  to  be 
derived  from  experiments  made  by  a  public  body. 


CHAPTER  III. 

THE  DISCUSSION  BEFORE  THE  SOCIETY  OF  CIVIL  ENGINEERS 

OF  FRANCE. 

ONE  of  the  most  complete  papers  upon  the  subject  of 
the  gas  turbine  which  have  yet  appeared  was  presented 
before  the  Society  of  Civil  Engineers  of  France,  on  February 
2,  1906,  by  M.  L.  Sekutowicz,  this  covering  a  thermody- 
namic  treatment  of  the  question  as  well  as  a  study  of  the 
gas  turbine  from  a  mechanical  point  of  view.  This  paper 
elicited  an  animated  discussion  which  included  the  views 
of  a  number  of  eminent  specialists  who  had  devoted  atten- 
tion to  the  subject,  the  whole  appearing  in  the  Memoires 
of  the  Society  for  February  1906. 

After  a  brief  historical  introduction,  M.  Sekutowicz 
proceeds  with  his  thermodynamic  study  as  follows :  * 

As  is  the  case  with  all  heat  motors,  the  gas  turbine  in- 
volves the  action  of  a  given  mass  of  a  determinate  fluid,  dur- 
ing a  unit  of  time,  between  certain  limits  of  pressure  and 
temperature. 

In  order  that  this  action  may  be  subjected  to  computa- 
tion it  is  necessary  that  each  of  its  phases  be  considered  as 
simple;  that  is,  characterized  by  the  constancy  of  some  one 
of  the  independent  variables  upon  which  the  state  of  the 
fluid  depends  at  each  instant,  such  as:  volume,  pressure, 
temperature,  and  entropy. 

The  phase  of  compression  may  be  adiabatic  or  isothermic. 
The  introduction  of  the  heat  may  he  isothermic  (as  in  the 
Carnot  cycle  and  its  derivatives),  or  isobaric  (combustion 
under  constant  pressure),  or  isopleric  (combustion  under 
constant  volume:  explosion).  The  expansion  will  be  adia- 
batic. Finally  the  rejection  of  the  heat  at  the  lower  tem- 

*  Mem.  Soc.  Ing.  Civ.  de  France,  Feb.  1906,  p.  204  et  seq. 
108 


THE   GAS   TURBINE. 109 

perature,  can  hardly  be  other  than  isobaric  or  isothermic 
(the  Carnot  cycle). 

The  first  two  phases  are  the  most  important,  for  the  last 
two  can  be  only  partially  realized  in  practice. 

In  fact  the  expansion,  in  the  case  of  the  gas  turbine, 
will  be  almost  rigorously  adiabatic,  while  the  rejection  of 
heat  can  only  take  place  at  constant  pressure  to  a  regenera- 
tor; or,  what  amounts  to  the  same  thing  as  regards  the  cycle, 
by  the  non-closure  of  the  cycle. 

We  then  have  six  principal  variants.  Besides  these  we 
may  examine  the  cycles  of  Stirling  and  of  Ericsson,  in  which 
the  adiabatics  of  Carnot  are  replaced  by  the  isodiabatics  and 
the  regenerative  cycles  derived  therefrom.  Finally  we  have 
to  study  the  effects  of  the  injection  of  water  or  of  cold  gases. 

Heat  motors  are  too  frequently  studied  with  regard  to 
the  extreme  temperature  limits  of  the  cycle.  There  results 
a  misleading  comparison  with  the  Carnot  cycle,  or  at  least 
a  comparison  which  fails  to  indicate  the  actual  development. 
What  really  concerns  us  is  the  value  of  the  thermal  efficiency 
/>,  the  mechanical  efficiency  >?,  and  the  total  useful  effect 
represented  by  their  product. 

Now,  as  we  shall  see,  these  efficiencies  are  not  always 
limited  by  the  extreme  limits  of  temperature.  Other  factors, 
no  less  important,  must  be  considered.  In  the  present  case 
these  are:  the  limits  of  pressure,  the  ratio  of  the  work  of 
compression  to  the  useful  work,  and  the  quantity  of  useful 
work  produced  by  a  kilogramme  of  air. 

The  lower  temperature  limit  is  usually  that  of  the  atmos- 
phere, and  may  be  taken  as  about  300°  C.  absolute.  The 
final  temperature  of  the  expansion,  however,  will  generally 
be  much  higher.  This  value  is  most  important,  since  it  is 
the  temperature  of  the  gases  delivered  upon  the  rotating 
metallic  portion  of  the  turbine. 

We  will  assume  that  the  turbine  wheel  can  be  so  con- 
structed as  to  stand  a  temperature  of  700°  C.  absolute, 


110  THE   GAS   TURBINE. 

without  injury.  This  fact  has  been  fully  demonstrated  in 
practice.  In  all  that  follows,  therefore,  we  shall  consider 
the  temperature  at  the  end  of  the  expansion  as  being  700°, 
except  when  examining  the  influence  of  variations  of  this 
factor. 

The  upper  temperature  limit  is  determined  largely  by 
the  heat  resistance  of  the  refractory  material  used,  not  only 
for  the  lining  of  the  combustion  chamber,  but  also  for  the 
construction  of  the  nozzle  in  which  the  expansion  takes  place. 
There  are  now  available  such  substances  as  carborundum, 
which  are  capable  of  resisting  the  highest  temperatures 
developed. 

Under  these  circumstances  the  maximum  temperature 
is  limited  by  the  following  conditions: 

1.  It  must  be  such  that,  with  the  degree  of  expansion 
attainable,   the   final   temperature   of   expansion   shall   not 
exceed  700°  C.  absolute. 

2.  It  must  be  attainable  by  the  combustion  of  ordinary 
fuels  with  a  sufficient  quantity  of  air  to  insure  a  complete 
combustion. 

As  is  well  known,  combustion  under  constant  volume 
produces  a  much  greater  elevation  of  temperature  than  is 
caused  by  combustion  at  constant  pressure.  Besides  this, 
when  the  compression  is  adiabatic  the  temperature  of  the 
gas  is  raised  to  a  greater  or  less  degree  before  combustion, 
this  effect  being  added  to  the  temperature  of  combustion. 
For  a  compression  of  30  atmospheres  the  temperature  will 
reach  800°  C.  absolute. 

Thus,  illuminating  gas  requires  5.5  times  its  volume  of 
air  in  order  to  enable  perfect  combustion  to  be  effected. 
If,  in  practice,  we  assume  that  6  volumes  of  air  are  required, 
1  kilogramme  of  the  mixture  will  evolve  574  calories.  Under 
these  conditions,  starting  from  the  ordinary  atmospheric 
temperature,  the  combustion,  if  conducted  at  constant 
volume,  would  produce  a  temperature  of  2450°  C.,  absolute. 


THE   GAS   TURBINE.  Ill 

If  the  combustion  takes  place  under  constant  pressure  the 
temperature  would  be  about  2000°  absolute.  With  acety- 
lene this  limit  may  be  extended.  With  other  gases  slightly 
different  results  are  obtained,  as  shown  hereafter. 

The  upper  limit  of  pressure  is  determined  almost  wholly 
by  practical  considerations.  As  we  shall  see,  it  is  without 
direct  influence  on  the  velocity  of  discharge.  If  the  com- 
pression is  isothermic  it  may  be  increased  without  increas- 
ing the  ratio  of  the  work  of  compression  to  the  useful  effect. 
We  may  consider  compressions  of  40  to  60  atmospheres 
(600  to  900  pounds  per  square  inch)  as  entirely  admissible, 
both  with  respect  to  the  compressor  and  the  combustion 
chamber. 

The  lower  limit  of  pressure  will  be  that  of  the  atmos- 
phere if  the  exhaust  is  made  into  the  open  air,  or  it  may 
be  a  very  low  pressure,  approaching  a  perfect  vacuum  if 
the  discharge  is  made  into  a  space  provided  with  an  air 
pump. 

The  ratio  of  the  work  of  compression  to  the  useful  effect 

C7»c 

=-  plays  an  important  part  in  the  gas  turbine,  because 
cr  u 

the  compressor,  being  necessarily  distinct  from  the  turbine, 
its  mechanical  efficiency  T}C  (which  includes  that  of  the 
transmission  mechanism  by  which  it  is  driven)  has  a  very 
marked  influence  upon  the  efficiency  of  the  entire  machine. 
When  this  ratio  is  very  high  the  importance  and  bulk  of  the 
compressor  occasions  some  practical  inconveniences.  A 
ratio  approaching  unity  is  practically  prohibitory. 

Finally,  the  quantity  of  useful  work  produced  per  kilo- 
gramme of  gas  gives  a  measure  of  the  specific  power  of  the 
machine. 

These  are  the  principal  elements  which  form  the  criterion 
in  the  discussion  which  follows.  But,  before  commencing 
this  discussion  it  remains  for  us  to  indicate  the  hypothesis 
and  the  numerical  data  upon  which  it  is  based.  In  this 


112  THE   GAS   TURBINE. 

connection  it  may  be  noted  that  all  the  computations  have 
been  made  with  the  slide  rule,  this  giving  a  degree  of  pre- 
cision quite  within  the  limits  of  error  of  the  premises. 

We  begin  with  the  simple  and  well-known  laws  of  ther- 
modynamics as  used  by  M.  Witz  in  his  classical  labors  upon 
the  gas  engine.  As  a  first  approximation  we  assume  the 
specific  heat  as  constant,  the  value  for  hot  air  at  constant 
pressure  CP  being  taken  at  the  usual  value  0.2375,  and  the 
specific  heat  at  constant  volume  cv  being  taken  as  0.1686, 
so  that  their  ratio  is 

r-^-i.4i. 

cv 

The  specific  constant  of  air  is  taken  at  29.3.  We  neglect 
the  contraction,  which  may  attain  5  per  cent. 

For  the  vapor  of  water  we  adopt  the  value  CP  =  OAS. 
It  is  only  in  special  cases  that  we  shall  take  into  account 
the  variation  of  specific  heat  with  the  temperature,  using 
the  linear  formula  of  M.  Lechatelier,  C  =  a+bT. 

We  shall  retain  for  adiabatic  expansion  the  formula  of 
Laplace  or  Poisson:pvy  =  constant. 

The  modern  exponential  formulas  are  very  interesting, 
but  their  use  would  burden  this  discussion  to  such  an  extent 
as  to  render  comparisons  impossible. 

After  having  cleared  away  the  general  discussion  we 
shall  return  to  the  special  modifications  to  which  our  results 
must  be  submitted  if  we  desire  to  follow  the  laws  of  gases 
to  a  higher  degree  of  precision. 

The  Mechanical  Efficiency  of  the  Gas  Turbine. 

We  have  to  consider  two  distinct  machines — the  turbine 
and  the  compressor,  each  having  its  own  efficiency.  More 
or  less  of  the  heat  energy  which  is  transformed  into  work 
in  the  turbine,  with  the  particular  efficiency  of  this  machine, 
is  expended  in  driving  the  compressor,  and  the  available 
power  is  only  the  difference  between  the  two  values. 


THE   GAS   TURBINE. 


113 


Thus,  let  Q  be  the  quantity  of  heat  furnished  by  the  com- 
bustion of  a  kilogramme  of  gas,  q  the  heat  rejected  with  the 
exhaust,  and  p  the  total  thermal  efficiency,  equal  by  defini- 


tion, to 


Q— q 
Q 


If  all  the  losses  are  reduced  to  losses  of  a 


thermal  order  there  will  be  produced  in  work : 


c  a  a 

FIG.  39. — Useful  work  and  work  of  compression. 

Now  let  ^c  be  the  theoretical  work  of  compression  per 
kilogramme  of  air  (this  being  computed  hereafter  for  each 
case),  and  let  TJC  be  the  mechanical  efficiency  of  the  com- 

cy^ft 

pressor,  defined  in  such  a  manner  that  —  is  the  quantity 

of  work  delivered  to  the  shaft  of  the  compressor  to  compress 
one  kilogramme  of  air.* 

On  the  other  hand  each  kilogramme  of  air  produces  in 
the  motor  turbine  a  quantity  of  " indicated"  work,  equal, 
by  definition,  to  the  sum  of  the  net  available  work  on  the 
shaft  and  all  the  passive  resistances  (friction,  etc.).  This 

*  In  the  case  of  isothermal  compression  the  theoretical  amount  of  work 
may  be  computed  by  the  law  of  Mariotte.  If  this  law  is  not  exactly  followed 
and  if  the  gas  is  slightly  heated  by  the  compression  the  corresponding  energy 
is  included  in  the  mechanical  losses  and  in  the  value  of  nc . 

8 


114 


THE   GAS   TURBINE. 


work  ^T,  which  we  shall  compute  for  each  case,  is  equal  to  the 
useful  work  'tfu,  denned  above,  increased  by  the  work  of  com- 
pression ^c,  as  we  shall  see  by  examining  the  diagram,  Fig.  39. 


i.oo 


080 


0.60 


040 


020 


Tc 
TT 

2.0 

1.8 

1.6 
1.4 
12 

1.0 

0^ 

1 

1 

/ 

Of 

7 

0.4 
02 

/ 

' 

/ 

^x 

x 

1 

0.4 


0.6 


0.8 


1.0Q= 


FIG.  40. — Values  of  efficiency  in  terms  of  tempera- 
ture ratio. 


0     0.2    0.4    0.6    0.8      1  I 
FIG.  41. — Values  of  tem- 
perature ratio  in  terms  of 
efficiency. 


The  indicated  power  furnished  by  the  motor  turbine, 
per  kilogramme  of  air,  is: 

*&  indicated  =  ^u  +  ^c.  (1) 

If  we  call  the  mechanical  efficiency  of  the  turbine  yt  the 
effective  work  on  the  shaft  will  be: 

^  effective  =  yt^u  +  «C"c) .  (2) 

It  follows  that  the  effective  work  available  upon  the  com- 
mon shaft  of  the  turbine  and  the  compressor,  supposing 
them  to  be  connected  thus  as  one  machine,  will  be: 

1^ 


*C"  net  work  = 


(3) 


If  the  compressor  be  driven  through  any  intermediate 
transmission  the  efficiency  of  this  transmission  should  be 
included  in  T)C. 


THE   GAS  TURBINE.  115 

The  mechanical  efficiency  of  the  two  machines  together 
will  then  be: 

net  work  /         IX^c  ,  > 


The  mechanical  efficiency  then  disappears  when 


For  example,  taking  7)t  =  r}c  the  efficiency  will  be  zero  for 


which  gives  the  following  values: 

7^  =  ^  =  0.5      0.6      0.7      0.8 
^  =  0.34     0.56     0.96     1.78 

We  shall  see  later  on  that  under  the  actual  conditions 
of  turbine  construction  yt  will  have  a  value  of  about  0.7. 

As  for  the  efficiency  of  the  compressor  i)c,  this  will  be 
for  improved  reciprocating  machines  0.8  to  0.9. 

Since  it  is  necessary,  however,  to  introduce  a  speed- 
reduction  transmission,  i)c  will  be  reduced  to  0.75  to  0.85. 

If  the  compressor  is  made  of  the  multicellular  turbine 
type,  permitting  direct  connection,  it  is  possible  that  the 
efficiency  will  be  in  the  neighborhood  of  0.6  to  0.7. 

If  we  take  rjt  =  rjc  =  0.7  we  see  that  the  mechanical  effi- 
ciency will  be  totally  annulled  for 

<TTc  =  cCw,  about. 
We  have  in  general 

7^=0.700-0.729^- 

This  shows  the  fundamental  importance  of  the  ratio  of  the 
work  of  compression  to  the  useful  work. 


116  THE   GAS   TURBINE. 

In  order  to  establish  our  ideas  in  this  respect,  we  may 
consider  theoretically  that  this  ratio  will  lie  somewhere 
between  0.2  and  0.4,  which  will  cause  the  total  mechanical 
efficiency  to  range  between  0.4  and  0.6.  As  we  shall  find 
the  thermal  efficiency  to  lie  between  0.4  and  0.6  we  see  that 
the  total  useful  efficiency  will  be  from  0.16  to  0.36. 

We  shall  now  pass  to  the  discussion  of  the  various  cycles 
applicable  to  the  gas  turbine. 

I. 
A.  Cycles  Using  the  Isothermic  Introduction  of  Heat. 

The  typical  cycle  of  this  group  is  that  of  Carnot.  Diesel 
has  sought  to  use  this  by  realizing  isothermal  combustion 
in  his  motor.  This  result  can  be  obtained  in  a  gas  tur- 
bine only  by  causing  the  combustion  to  be  continued  in  the 
expansion  nozzle,  or  by  causing  the  expansion  to  take  place 
in  several  stages  with  successive  interheaters.  This  last 
solution,  however,  would  only  be  an  approximative  one. 

The  Carnot  Cycle. 

The  kilogramme  of  gas  under  consideration  is  compressed 
from  p0  to  pt  maintaining  at  the  same  time  the  initial  tem- 
perature T0.  This  isothermal  compression  absorbs  a  quan- 
tity of  work  ^i,  given  by  the  equation: 

c£i  =  RT0  log  hyp 

The  gas  is  now  compressed  adiabatically  from  p1  to  p2. 
The  temperature  passes  from  T0  to  T2  and  the  work  absorbed 
by  the  compression  is 


We  also  have: 


THE   GAS  TURBINE. 


117 


We  then  introduce  the  quantity  of  heat  Q  upon  the 
isothermal  CD,  at  the  temperature  T2,  during  which  period 
the  pressure  falls  from  p2  to  pr 

We  then  have: 


We  know  that  the  thermal  efficiency  of  the  Carnot  cycle 

is  equal  to: 

T 


FIG.  42.— The  Carnot  cycle. 

and  that  the  useful  work  is: 


We  also  have: 


,ART2. 


Po     Ps 


The  properties  of  the  cycle  depend  only  upon  the  tern- 

/v\ 

perature  of  combustion  T2,  the  total  compression  ratio  — , 

Po 
and  the  introduction  of  the  heat  Q.     The  temperature  of  the 

exhaust  is  that  of  the  atmosphere,  about  300°  C.  absolute. 


118 


THE   GAS  TURBINE. 


The  thermal  efficiency,  which  depends  only  upon  T2, 
may  reach  very  high  theoretical  values,  but  to  attain  these 
involves  the  use  of  excessively  high  compressions;  thus: 


Temperature  of  combustion  T2 

300 

600 

900 

1200 

1500 

1800 

2100 

Thermal  efficiency  p 

o 

050 

066 

075 

080 

083 

086 

Adiabatic  compression  ratio  — 

1 

11 

46 

128 

282 

525 

913 

We  see  that  it  is  impossible  to  pass  a  thermal  efficiency 
of  0.66  without  being  obliged  to  have  recourse  to  excessive 
compressions,  since  it  is  necessary  to  multiply  the  adiabatic 
compression  ratio,  which  we  shall  calculate. 


2500 


FIG.  43.  —  Efficiency  and  ratio  of  adiabatic  compression.    Carnot  cycle. 


This  latter  :       is  a  function  of       .     For  T2  =  900  degrees, 

Pi  1  2 


and  Q=300  calories,  we  have:     r  =  0.333,  and 

J-  •> 


*  =  120. 
Po 


THE   GAS  TURBINE.  119 

The  ratio  of  the  work  of  compression  to  the  useful  work 
is  given  by: 


whence: 


2  _  i 
T 

1  0 


In  our  particular  case  we  have: 


We  have  seen  above  that  the  mechanical  efficiency  dis- 
appears as  the  ratio  between  the  work  of  compression  and 
the  useful  work  approaches  unity.  As  a  matter  of  fact  we 
cannot  even  admit  sufficiently  high  values  for  the  thermal 
efficiency  and  for  the  temperature  T2,  since  the  latter, 
resulting  from  the  adiabatic  compression,  cannot  exceed 
700  degrees  C.  absolute,  whether  we  employ  a  reciprocating 
piston  compressor  or  a  rotary  turbine  compressor. 

The  Carnot  cycle  is  therefore  not  adapted  to  the  gas 
turbine,  since  the  high  thermal  efficiency  which  can  be  real- 
ized by  its  use  is  obtainable  only  by  the  employment  of 
very  high  compressions  and  enormous  masses  of  gas.  In 
consequence,  the  compressor,  which  is  admittedly  the  weak 
point  of  the  gas  turbine,  assumes  an  excessive  importance, 
and  the  mechanical  losses  would  absorb  all  the  useful  work. 

The  Diesel  Cycle. 

Theoretically  the  cycle  of  Diesel  differs  from  the  Carnot 
cycle  by  the  substitution  of  a  wholly  adiabatic  compression 
for  the  two  successive  compressions,  isothermal  and  adia- 


120 


THE   GAS  TURBINE. 


batic,   of  Carnot.     The   rejection   of   heat   to   the   cooling 
medium  is  thus  produced  by  the  non-closure  of  the  cycle : 
Here  again  the  isothermal  expansion  is  defined  by: 

Q 


ART* 


Pa 


and  a  considerable  degree  of  expansion  is  required  to  enable 
a  sufficient  quantity  of  heat  Q,  to  be  introduced. 


FIG.  44.  —  The  Diesel  cycle. 

Even  if  we  admit  that  the  temperature  of  combustion, 
obtained  at  the  end  of  the  adiabatic  compression,  may 
attain  800  degrees  (corresponding  to  a  compression  of  35 
atmospheres),  we  have,  for: 

Q  =  100     200     300  calories 


Ps 


37     220 


We  cannot  therefore  exceed  an  introduction  of  200  calories, 
and  even  at  this  figure  there  would  no  longer  be  an  adiabatic 
expansion. 

The  maximum  temperature  of  the  cycle  should  therefore 
occur  at  the  beginning  of  the  combustion,  and  should  be 
superior  to  that  produced  by  the  compression,  and  thus 
the  curve  of  combustion  should  keep  above  the  isothermal. 

In  any  case  this  cycle  is  not  adapted  to  the  gas  turbine. 


THE   GAS   TURBINE. 


121 


Partial  Isothermal  Cycles.— Some  writers,  Barkow  among 
others,  have  suggested  that  the  combustion  should  be 
started  under  constant  pressure,  and  completed  isother- 
mically.  We  shall  examine  this  solution  later  on,  but  it  is 
difficult  of  realization  in  turbines,  and  offers  no  especial 
advantages. 

B.    Cycles  Using  the  Isobaric  Introduction  of  Heat. 

Combustion  under  Constant  Pressure. — With  combustion 
at  constant  pressure  the  temperature  of  the  gas  is  raised. 
It  is  preceded  by  a  compression  which  may  be  either  adia- 
batic  or  isothermic.  In  the  first  case  the  compression  is 
not  accompanied  by  the  transfer  of  any  heat  to  the  cooling 
medium,  but  it  involves  the  expenditure  of  a  greater  amount 
of  work.  A  complete  computation  is  necessary  to  show 
which  of  the  two  systems  should  be  adopted.  The  follow- 
ing table  will  serve  as  a  basis  for  the  calculations : 


Compression  ratio. 

5 

10 

15 

20 

25 

30 

40 

60 

80 

100 

Final  temperature  of  adiabatic  compression  .  . 

479 

585 

658 

716 

764 

804 

875 

990 

1040 

1150 

Equivalent  in  calories  of  work  (  adiabatic  — 

42 

68 

85 

99 

110 

120 

136 

164 

176 

203 

of  compression         ,               1  isothermal  .  . 

33 

48 

56 

62 

67 

71 

76 

85 

90 

95 

Ratio  of  the  two  efforts  

0.78 

070 

0.66 

0.62 

0.61 

0.59 

0.56 

0.52 

0.51 

0.48 

These  figures  are  calculated  upon  the  assumption  of  an 
initial  temperature  of  300  degrees  C.  absolute,  and  result 
in  the  following  considerations: 

The  work  absorbed  by  the  compressor  consists  of  the 
compression,  properly  so-called,  which  is  given,  in  the  case 
when  operating  at  constant  temperature,  by  the  formula 


and  the  work  necessary  to  drive  the  compressed  air  into 
the  reservoir  at  the  pressure  p^  that  is  pl  v^ — p0  VQ. 


122 


THE   GAS   TURBINE. 


But  in  this  case  the  second  term  is  zero,  and  we  have 


IL 


5  cr 


150 


100 


50 


10 


ZO 


30 


40  50 


60 


70  80 

Pressures 


FIG.  45.  —  Equivalent  in  calories  of  the  work  of  compression  per  kilogramme  of  air. 

In  the  case  of  the  adiabatic  compression  the  first  term 
has  a  value  ECV(T1  —  T0),  and  the  second  (plvl  —  pQv0)  is  equal 
to  R(Tl—TQ),  whence: 


and  since 
we  have: 


E(CP—cv) 


From  this  it  follows  that: 

«  *  lo 


'(IT-1 


THE   GAS   TURBINE.  123 

This  ratio  tends  to  approach  unity  for  infinitely  small 
compressions.  It  decreases  rapidly  as  the  compression 
ratio  increases,  and  falls  to  0.5  for  a  compression  of  about  80. 

The  power  absorbed  by  the  compressor  is  therefore  less, 
for  the  same  compression,  with  the  isothermal  method  than 
with  the  adiabatic.  This  difference  is  still  more  marked 
if,  for  any  reason,  the  gas  which  has  been  compressed  adia- 
batically  is  allowed  to  return  to  its  initial  temperature. 
Thus  a  compression  of  20  will  drop  to  about  8.4.  This  fact 
renders  adiabatic  compression  inadmissible  for  the  ordinary 
applications  of  compressed  air.  In  the  case  of  the  gas  tur- 
bine, however,  the  sensible  heat  of  the  adiabatically  com- 
pressed gas  is  not  lost,  and  a  fuller  discussion  of  the  subject 
becomes  necessary. 

Adiabatic  Compression. 

During  the  compression  the  pressure  passes  from  p0  to 
Pi  and  the  temperature  from  T0  to  Tr 

T 
We  have:  fe- 

Po     \T 

The  introduction  of  Q  calories,  at  the  constant  pressure 
pv  raises  the  temperature  to  T2,  the  temperature  of  combus- 
tion, and 

Q  =  CP(T2-Tl). 

The  mixture  then  expands  adiabatically  from  T2  to  T3,  and 


r, 

We  see  that: 


The  quantity  of  heat  rejected  to  the  cooling  medium  is 
equal  to  the  heat  carried  off  by  the  exhaust  gases,  that  is: 


124 


THE   GAS   TURBINE. 


The  thermal  efficiency  p  will  then  be : 

_Q-q_    _T0 

p-    Q  ¥• 

We  therefore  obtain  the  same  efficiency  as  in  a  Carnot 
cycle  having  the  same  ratio  of  adiabatic  compression,  but 
without  having  the  necessity  for  the  preliminary  isothermal 
compression. 


FIG.  46. — Cycle  of  isobaric  combustion  with  adiabatic  compression. 

The  total  compression  is  therefore  much  lower,  but  the 
upper  temperature  of  the  cycle  is  much  higher,  a  matter 
which  offers  no  inconvenience. 

The  ratio  of  the  work  of  compression  to  the  useful  work 
is  given  by 

TO^T"      l~^     Cv~^' 

It  is  easy  to  see  that  this  ratio  is  constant  if  we  give  the 
temperature  T3  at  the  end  of  the  expansion  a  fixed  value, 

rwi  rji 

for  we  have  7^  =  7^,  and  consequently : 

^3  -*  0 


THE   GAS   TURBINE. 


125 


This  ratio  attains  greater  value,  therefore,  as  the  tem- 
perature T3  has  a  higher  value.  Since,  however,  for  con- 
structive reasons,  T3  cannot  be  allowed  to  exceed  700  degrees 
C.,  we  have: 

C7«V.  1 

=  0.75 


^u     700_ 
300 

The  corresponding  value  of  the  total  mechanical  effici- 
ency T),  given  by  the  equation  ^=0.700 — 0.729^,  is  there- 
fore only  about  0.15. 

The  properties  of  the  most  advantageous  family  of  cycles 
are  given  below: 


Ratio  of  compression  — 

5 

10 

15 

20 

30 

Final  temperature  of  compression  Tt  

480 

585 

658 

716 

804 

Final  temperature  of  combustion  T2  

1120 

1400 

1540 

1670 

1876 

Final  temperature  of  expansion  Tt  .  . 

700 

700 

700 

700 

700 

Heat  introduced  (calories)  Q 

149 

188 

205 

227 

255 

Heat  lost  in  the  exhaust  q  

92 

92 

92 

92 

92 

Thermal  efficiency  p 

0  37 

0  49 

054 

0  58 

063 

Equivalent  A^c  of  work  of  compression  . 
Equivalent  A*Cu  of  useful  work  .  . 

42 

56 

68 
94 

85 
112 

99 
134 

120 
162 

Total  useful  effect  py 

0  06 

0  08 

0  086 

0  092 

0  10 

Equivalent  An*Gu  of  net  mech.  work   .... 
Consumption  of  air  per  H.P.  hour,  kg  

Ratio  of  powers  -  —  -  

8.4 
75 

7  1 

14.1 

45 

7  1 

16.8 
37 

7  1 

20 
32 

7  1 

24.3 
26 

7  i 

These  results,  plotted  in  the  diagram,  are  not  very 
encouraging.  An  adiabatic  compression  of  20  gives  a  final 
temperature  of  716,  which  should  not  be  exceeded.* 

The  useful  effect  does  not  exceed  9  per  cent.,  and  the  mass 
of  gas  required  to  produce  a  unit  of  work  is  considerable. 

*  That  is,  if  the  action  is  truly  adiabatic,  without  any  artificial  cooling  of 
the  parts  in  contact  with  the  gas.  If  this  is  not  the  case  it  is  impossible  to  cal- 
culate accurately  the  results  which  may  be  attained. 


126 


THE   GAS   TURBINE. 


§ 

~ 

°   CO           **- 

s 

CO 

8 

O 

1O 

d 

%  § 

d  d 

0 
00 

P  s  ^  »  § 

s 

1 

o 

1O 

d 

8  S 

d  d 

o 

<O   nn   £^   1O   co 

§3  $  °>  °°  d 

£ 

1 

o 

d 

CO   00 

d  d 

o 
"t 

|  g  8  g  | 

S 

§ 

rH 
CO 

o 

d 

00   IO 
C^J   O5 

d  d 

s. 

3 

QQ    JO    C<J    rH    CD 

00   „   05       g 

g 

a 

CO 

o 

d 

i  o 

d  ^ 

i 

1C 

o  o       "^ 

t-   w   OS   CO   g 

S 

s 

o 

1 

CO 

°1   rH 

O 

i 

s 

rH    °°    ^    ^    O 

S 

a 

d 

d 

S?  c^ 

"^   rH 

O 

H 

2 

J5   <M   G*   *°   o 

s 

rH 

O5 

S 

d 

O   CO 

d 

-e 

O 

lO   ,             lO 
CO   ^   G^l   CO   rt< 

»  S  »  *  d 

00 

rH 
r-t 

d 

% 

d 

OQ 

d  ^ 

i 

rd 

1C 

§  1  §  g?  s 

rH   ^             O 

co1 

g 

d 

d 

rH    °°. 

d  ^ 

g 

g 

| 



• 

• 

h| 

'i 

.0 

S 

« 

02 

&J5 



Compression  ratic 

Temperature  of  combustion  T2  .  . 
Heat  introduced  (calories)  Q  .  .  . 
Heat  lost  in  the  exhaust  q  
Heat  lost  in  the  compression  Q  ' 
Thermal  efficiency  p  

Equivalent  A""Cc  of  work  of  com] 

Equivalent  A  ^u  of  useful  work 

.2 

i 

Mechanical  efficiency  rj  

g;^  a 

-feife; 

1  | 

!  1 

3  1 
^  (§ 

THE   GAS   TURBINE. 


127 


100 


050 


seful  effect 


-d-Ltp£rH.Phour_ 


2000° 


1000° 


11K8 


10 


15 


20% 


PIG.  47. — Cycles  with  adiabatic  compression  and  isobaric  combustion.    Exhaust  discharged 

at  700  degrees  C. 

Isothermal  Compression. 

The  isothermal  compression  from  p0  to  plt  effected  at  a 
temperature  T0,  absorbs  a  quantity  of  work  of  which  the 
equivalent  in  heat  is: 


128 


THE   GAS   TURBINE. 


The  introduction  of  Q  calories,  at  the  constant  pressure 
plt  raises  the  temperature  to  T2,  and: 


The  adiabatic  expansion  from  pl  to  pQ  brings  the  tempera- 
ture to  T3,  and 


/PoV 
2     \pj 


The  exhaust  gases  carry  off  with  them  heat  equal  in 
calories  to: 


Reheating 


Cooling 


FIG.  48.  —  Cycle  with  isobaric  combustion  and  isothermal  compression. 

The  thermal  efficiency  will  therefore  be: 

Cf(Tt-  T,)  -CP(T3-  T,)ART0  log  hyp-' 


cp(:r2-r0) 

The  table  on  page  125  gives  the  results  of  computations 
for  a  series  of  cycles  having  the  same  temperature  of  exhaust, 
7^3  =  700°  C. 

These  results  show  that  it  is  important  to  use  as  high  a 
compression  as  possible.  In  this  respect  the  limits  are 
those  imposed  by  the  values  for  the  temperatures  of  com- 


THE   GAS   TURBINE.  129 

bustion  and  of  the  introduction  of  the  heat,  these  becoming 
excessive  when  the  total  compression  passes  60. 

In  this  case  the  results  may  be  ameliorated  by  admitting 
a  lower  temperature  for  the  exhaust.  For  example,  let  us 
take  a  compression  of  80.  Let  the  temperature  of  the  ex- 
haust be  placed  at  600°  absolute,  instead  of  700°. 

The  temperature  of  combustion  will  then  be  2150°.  We 
also  find  that  the  temperature  Q  of  introduction  of  the 

C7»c  QQ 

heat  will  be  440,  the  efficiency  0.635,  the  ratio  c 


0.325,  whence  77  =0.46,  and  consequently  py  =0.29;  while 
we  should  have  had  0.28  with  a  compression  of  40,  and  an 
exhaust  temperature  of  700°  absolute. 

There  would  be  no  theoretical  advantage  in  thus  lower- 
ing the  temperature  of  the  exhaust,  if  it  did  not  have  the 
practical  value  of  aiding  in  the  use  of  successive  pressure 
stages  in  the  turbine.  By  the  use  of  this  system,  however, 
we  may  carry  the  expansion  down  to  700°  in  the  nozzles  of 
the  first  turbine,  and  continue  it  from  700°  to  600°  in  the 
guide  blades  of  a  second  group  of  revolving  wheels. 

A  series  of  practical  tests  would  be  required  to  deter- 
mine the  exact  limit  from  which  high  compressions  could  be 
utilized  in  this  manner.  This  limit  will  be  found  to  depend 
both  upon  the  true  law  governing  the  expansion  and  upon 
the  temperature  of  combustion  actually  attainable*. 

Below  this  limit  it  will  not  be  found  advantageous  to 
attempt  to  utilize  high  compressions  by  the  reduction  of 
the  temperature  of  the  exhaust,  and  it  will  be  a  better  en- 
deavor to  increase  the  introduction  of  the  heat  and  the 
maximum  temperature. 

It  does  not  seem  to  be  a  practical  impossibility  to  realize 
higher  compression  ratios  than  50.  The  construction  of  the 
compressors  and  the  combustion  chambers  for  such  pressures 
seems  practicable. 

*  The  values  for  7,  and  for  the  specific  heats,  may  differ  in  practice  from 
those  which  have  been  taken  in  the  computations. 

9 


130 


THE   GAS   TURBINE. 


But  the  actual  pressure  may  be  modified  by  causing  the 
exhaust  gases  to  be  discharged  at  a  lower  pressure.  This 
point  will  be  considered  more  fully  hereafter,  and  it  is  now 
only  necessary  to  mention  that  the  lower  pressure  p0  may 
be  made  less  than  atmospheric  pressure  (such  as  J,  },  or  -J- 
atmosphere)  without  in  any  way  changing  the  preceding 
arguments  and  calculations.  The  upper  pressure  limit  pl 
will  then  be  reduced  to  J,  J,  or  i  of  its  former  value.  The 

sr\ 

ratio  —  will  not  be  changed,  and  the  efficiencies  will  not  be 

Po 

modified. 

/*> 


T,; 


o  v 

FIG.  49. — Cycle  with  isobaric  combustion  and  isothermal  expansion. 

We  may  mention  here  a  modification  suggested  by 
Barkow  among  others,  in  which  the  combustion,  commenced 
under  constant  pressure,  is  completed  in  the  course  of  an 
isothermal  expansion. 

Let  us  suppose  the  adiabatic  expansion  is  the  same  as 
in  the  preceding  case,  and  the  final  temperature  700°  C. 
absolute.  It  follows  that  the  upper  temperature  limit  will 
be  the  same,  and  consequently  also  the  quantity  of  heat  Q, 
introduced  under  constant  pressure.  But  we  may  introduce 
a  supplementary  quantity  of  heat  K,  during  the  isothermal 
expansion.  Let  /  be  the  ratio  of  this  expansion,  we  will 
then  have:  K  =  ART2  log  hyp  (/). 


_  THE   GAS   TURBINE.  _  131 

The  total  compression  will  be  /-times  greater  than 
before,  so  that  the  work  of  compression  will  be  increased 
by  a  supplementary  amount 


There  will  then  be  a  gain  of  work  equal  to: 
AR(T2-T.}  log  hyp  (*)  or  ^~^K. 

1  2 

The  quantity  of  heat  introduced  at  constant  temperature 
is  then  utilized  with  a  thermal  efficiency  equal  to  that  of  the 
Carnot  cycle,  so  that  the  efficiency  of  the  entire  cycle  is  im- 
proved. It  is  necessary,  however,  to  give  a  considerable 
value  to  /,  in  order  that  K  may  obtain  any  importance. 
A  complete  computation  shows  that  it  would  be  better, 
so  far  as  the  total  useful  effect  is  concerned,  to  utilize  all 
the  compression  available  to  raise  to  a  maximum  the  intro- 
duction of  heat  under  constant  pressure. 

Discussion  of  Comparative  Efficiencies. 

We  may  now  make  a  definite  comparison  of  the  two 
modes  of  compression. 

It  will  be  seen  at  once,  by  an  inspection  of  the  diagram, 
that  the  thermal  efficiency  p  is  slightly  greater  when  we 
use  adiabatic  compression.  But  since,  with  this  system  we 
cannot  exceed  in  practice  a  compression  ratio  of  20,  the 
maximum  value  for  p  is  0.58;  while  when  the  compression 
is  isothermal,  we  may  carry  the  compression  as  high  as  60, 
which  gives  for  p  the  maximum  value  0.63. 

The  superiority  of  isothermal  compression  is  still  more 
marked  from  the  point  of  view  of  the  mechanical  efficiency. 
While  this  remains  constant  whatever  the  compression  in  the 
adiabatic  system,  it  increases  with  the  compression  in  the  iso- 
thermal system,  and  attains  values  ranging  from  double  to 
triple  those  realized  in  the  first  case.  The  same  is  practically 
true  with  regard  to  the  total  efficiency  py,  which,  according 
to  our  hypotheses,  appears  to  have  a  limit  of  about  0.30. 


132 


THE   GAS   TURBINE. 


It  will,  therefore,  be  necessary  to  expend  2120  calories 
per  effective  horse-power  hour,  delivered  on  the  shaft,  which 
corresponds  to  a  consumption  of  212  grammes  of  hydro- 
carbon fuel,  having  a  calorific  value  of  10,000  calories  (lower 
calorific  value).  The  Diesel  and  the  Banki  motors  have  a 
consumption  of  180  to  250  grammes.  Gas  engines  operating 
with  blast-furnace  gas  require  at  a  minimum  about  2000 
calories  per  effective  horse-power. 

The  fuel  consumption  of  the  gas  turbine  is  therefore 
comparable  with  that  of  the  best  motors  known.  The  weak 
point  appears  in  the  fact  that  the  effective  power  absorbed 
by  the  compressor  is  equal  to  about  85  per  cent,  of  the  net 
effective  power  practically  available  on  the  shaft. 

^It  should  be  noted  that  if,  by  reason  of  the  defective 
arrangement  of  the  compressor,  the  heat  developed  during 
the  compression  is  not  immediately  absorbed  by  the  injection 
of  water  and  by  cooling  the  walls,  but  only  disappears  in  the 
flow  of  the  gas  between  the  compressor  and  the  turbine,  the 
efficiency  will  be  much  less  than  in  the  two  preceding  cases./ 

We  have,  in  fact,  the  following  results:  the  ratio  of  the 
work  of  compression  to  the  useful  work  will  be  constant 
whatever  the  degree  of  compression  for  any  given  tempera- 
ture of  exhaust.  For  an  exhaust  temperature  of  700°  C. 
absolute,  this  ratio  is  0.75,  whence  y  =0.17.  As  for  the  ther- 
mal efficiency,  it  will  vary  as  shown  in  the  following  table : 


Ratio  of  compression. 

5 

10 

15 

20 

30 

40 

60 

80 

100 

Heat  introduced   Q 

195 
42 
61 
0.31 
0.053 

254 
68 
94 
0.37 
0.063 

292 

85 
115 
0.39 
0.067 

328 
90 
137 
0.44 
0.071 

375 
120 
163 
0.44 
0.074 

415 
136 
187 
0.45 
0.077 

480 
164 
224 
0.47 

0.080 

522 

176 
254 
0.49 
0.083 

563 
202 

271 
0.49 
0.080 

Heat  lost  in  compression,  Q' 
Equivalent  ^L^w,  useful  work 
Thermal  efficiency  p 

Total  useful  effect  pn  •  • 

The  results  would  not  be  as  low  as  indicated  in  the  table 
if  the  compression  were  effected  in  several  stages,  because 
the  cooling  of  the  gas  between  the  cylinders  reduces  the 


THE   GAS   TURBINE. 


133 


expenditure  of  work.  It  might  be  possible  to  obtain  a 
satisfactory  result  if  the  compression  were  divided  into  a 
number  of  stages,  with  complete  inter-cooling. 

Cycles  with  Isopleric  Introduction  of  Heat. 
(Cycles  for  Explosion  Motors.) 

Without  discussing,  for  the  moment,  whether  or  not  this 
method  is  practically  applicable  to  the  gas  turbine  we  may 
examine  the  efficiencies  which  it  is  theoretically  capable  of 
realizing. 

The  introduction  of  heat  at  a  constant  volume  causes 
an  increase  of  pressure,  and  produces  a  greater  rise  of  tem- 
perature than  if  a  constant-pressure  system  is  employed. 

Adiabatic  Compression. 

If  the  compression  is  effected  adiabatically  the  final 
temperature  of  the  explosion  will  be  very  high,  and  the 
introduction  of  heat  per  kilogramme  of  gas  cannot  be  very 
great.  In  fact  we  are  obliged  to  require  excessive  final 


Ratio  of  compression  — 
Po 

i 

5 

10 

15 

20 

Final  temperature  compression  !7\  

300 
980 
115 
0.200 
0 
23 

0 

0.70 
0.140 

0 

3.27 

16 
39.5 

480 
1530 
188 
0.505 
42 
96 

0.44 

0.38 
0,192 

1.66 

15.4 

36.5 
17.4 

585 
1930 
230 
0.595 

68 
138 

0.50 

0.34 
0.203 

2.1 

32.7 

47.0 
13.6 

655 

2190 
260 
0.645 

85 
168 

0.52 

0.32 
0.210 

2.3 

49 

54.0 
11.8 

717 
2300 
270 
0.654 
99 
178 

0.55 

0.30 
0.200 

2.6 

65 

54.0 
11.8 

Final  temperature  combustion  T2  

Heat  introduced  Q  (calories) 

Thermal  efficiency  p 

Equivalent  A  eCc  of  work  of  compression  . 
Equivalent  A^Tu  of  useful  work  .         ... 

Ratio  ~ 

TO* 
Mechanical  efficiency  f)  

Total  useful  effect  pri   .  .  .  . 

Nc 
Ratio  of  power  —  .  .                       .... 

Ratio  of  pressures  —  .  . 

Po 
Net  available  mechanical  work  77  TO*  
Consumption  of  air,  kg.  per  H.P.  hour.  .  . 

134 


THE    GAS   TURBINE. 


*fe 

I 
loo" 


050 


i 


•% 


2000° 


1000° 


10 


20 


FIG.  50. — Cycle  with  adiabatic  compression  and  isopleric  combustion.    Exhaust  escaping 
at  700  degrees  C.  absolute. 

explosion  pressures  in  order  to  attain  the  temperature  of 
700°  at  the  end  of  the  expansion.  It  is  therefore  impractica- 
ble to  exceed  a  compression  ratio  of  15,  which  leads  to  an 
explosion  pressure  of  49  atmospheres.  Under  these  condi- 
tions, themselves  difficult  to  realize,  the  thermal  efficiency 


THE   GAS   TURBINE.  135 

p  will  be  about  0.64,  with  a  mechanical  efficiency  of  0.33 
and  a  useful  effect  of  0.21,  as  shown  in  the  table  on  page  133, 
which  gives,  as  before,  the  results  of  a  series  of  cycles,  for 
an  exhaust  temperature  of  700°  C.  absolute. 

Explosion  turbines  with  adiabatic  compression  have, 
therefore,  a  low  efficiency,  the  total  useful  effect  not  exceed- 
ing 20  per  cent.  Increase  of  initial  compression  has  but  a 
slight  influence,  so  that  such  machines  are  of  interest  only 
for  small  powers,  or  in  cases  in  which  the  consumption  of 
fuel  is  a  secondary  consideration. 

Isothermal  Compression. 

In  this  case  we  introduce  a  quantity  of  heat  Q  for  each 
kilogramme  of  gas  and  have: 


The  pressure  becomes 


The  adiabatic  expansion  brings  the  temperature  down 
to  T3. 

We  then  have: 


^2 

and  T.  =  — 


The  heat  discharged  to  the  cooling  medium  is  composed 
of  the  calories  rejected  with  the  exhaust:  CP(T3 — T0)  and 
the  heat  subtracted  during  the  isothermal  compression: 


RTQ  log  hyp  M^J.     The  thermal  efficiency  will  then  be: 

cv(T2-T0)-Cp(Ts-  T0)—RT0  log  hypf^-1 
P  = V^o 


136 


THE   GAS   TURBINE. 


o   '  v 

FIG.  51. — Cycle  with  isopleric  combustion  and  isothermal  compression. 

If,  as  before,  we  take  the  exhaust  temperature  at  700°  C. 
.,  we  have  the  corresponding  family  of  cycles  as  follows: 


Compression  ratio  — 

1 

s 

10 

15 

20 

Temperature  of  compression  T2          

980 

1820 

2420 

2850 

3210 

Heat  introduced.  Q  (calories) 

115 

255 

355 

430 

490 

Heat  lost  in  the  exhaust  q  

92 

92 

92 

92 

92 

Heat  lost  in  the  compression 

0 

33 

48 

56 

62 

Thermal  efficiency  p 

019 

051 

061 

066 

068 

Equivalent  A  ^c  of  work  of  compression  . 
Equivalent  A^u  of  useful  work    

0 
23 

33 
130 

48 
215 

56 

282 

62 
336 

r>   *•      ^ 

Katio  .                       

0 

025 

0.22 

020 

019 

^u 
Mechanical  efficiency  y  .   .            

070 

052 

0.54 

0.55 

056 

Total  useful  effect  prj               .... 

0  13 

0265 

033 

0365 

038 

Nc 
Ratio  of  powers  •  —  . 

o 

068 

058 

052 

049 

Ratio  ^ 

327 

6.1 

8.1 

9.5 

10.7 

Pi 
Ratio  ^2.. 

3.27 

30.4 

80.7 

143 

214 

Po 

Net  available  mechanical  work  ^'Cw  
Consumption  of  air,  kg.  per  H.P.  hour  .  .  . 

16 
39.5 

68 
9.4 

116 
5.5 

156 
4.1 

188 
3.4 

_  THE   GAS   TURBINE.  _  _  137 

The  ratio  of  the  work  of  compression  to  the  useful  work 
is  low,  which  is  a  great  advantage.  But  with  even  a  com- 
pression ratio  of  10  the  final  pressure  passes  80  atmospheres, 
a  limit  very  difficult  to  handle.  The  total  useful  effect  then 
reaches  0.38,  while  with  isothermal  compression  followed 
by  combustion  at  constant  pressure  the  limit  is  0.31. 

If  the  exhaust  is  discharged  into  a  space  having  a  reduced 
pressure  it  becomes  practicable  to  use  higher  pressure  ratios. 
Thus,  with  a  compression  of  3  and  an  introduction  of  430 
calories,  the  maximum  pressure  reaches  28.5  atmospheres. 
If  we  allow  this  to  escape  into  a  space  having  a  pressure  of 
i  atmosphere  we  get  a  total  expansion  of  143  times,  this 
being  necessary  to  reduce  the  temperature  of  the  gas  from 
2850°  to  700°  absolute,  which  gives  a  useful  effect  of  0.365, 
while  the  power  of  the  compressor  will  be  reduced  to  about 
one-half  the  net  available  power.  These  results  are  very 
encouraging.  Unfortunately,  it  is  not  easy  to  construct  a 
satisfactory  explosion  turbine,  the  operative  portions  of 
the  explosion  chamber  being  unable  to  resist  the  very  high 
temperatures  developed. 

It  may  readily  be  shown  that  the  efficiency  becomes  less 
favorable  if  the  temperature  of  the  exhaust  is  made  lower 
than  700  degrees. 

Isopleric  Combustion  Cycles  without  Compression. 

If  the  gas  is  not  compressed  before  the  explosion  the 
efficiency  is  low,  as  we  have  already  seen.  We  may  investi- 
gate the  manner  in  which  it  varies  if  the  temperature  T3  of 
the  exhaust  is  varied. 

We  have: 

T7   ,  _  HP  rp   _  rp 

3 


It  is  easy  to  see  that  efficiency  will  be  a  minimum  when 
T0,  and   increases   with  the   increase  of    T3  above  its 


minimum  value  T0. 


138 


THE   GAS   TURBINE. 


For 

We  have 
and  hence 


600 

0.16 

0.11 


800 

0.23 

0.16 


1000 
0.27 
0.17. 


^=0.04 

We  see  that  the  highest  efficiency  corresponds  to  the 
highest  temperature  of  the  exhaust  admissible,  with  regard 
to  the  endurance  of  the  metallic  turbine  wheel.  Under  the 
most  favorable  conditions  the  total  efficiency  cannot  be 
expected  to  surpass  14  per  cent. 

II. 

Cycles  with  Expansion  Prolonged  below  Atmospheric 
Pressure. 

In  the  cycles  thus  far  examined  the  gas  has  been  ex- 
panded down  to  the  pressure  of  the  atmosphere  and  rejected 
at  a  temperature  dependent  upon  the  conditions  of  opera- 
tion; chosen,  however,  as  high  as  possible,  with  respect  to 


FIG.  52. — Cycle  with  prolonged  expansion. 

the  endurance  of  the  turbine  wheel.  There  is,  however, 
nothing  to  prevent  the  arrangement  of  the  parts  in  such  a 
manner  as  to  cause  a  part  of  the  process  to  be  conducted 
at  a  pressure  below  that  of  the  atmosphere;  as  has  already 
been  done  in  the  so-called  "atmospheric"  gas  engines,  using 
a  free  piston. 


THE   GAS   TURBINE. 


139 


In  the  case  of  the  turbine  this  may  be  effected  by  the 
use  of  an  air  pump.  When,  however,  the  large  dimensions 
are  considered,  a  piston  pump  is  seen  to  be  unsuited  for 
this  purpose.  It  is  necessary,  therefore,  to  use  multicellular 
turbine  machines  similar  to  those  already  designed  for  com- 
pressors. For  a  reduction  of  the  pressure  to  i  atmosphere 
it  will  not  be  found  necessary  to  use  more  than  five  turbine 
wheels.  In  order,  however,  to  reduce  the  amount  of  work 
absorbed  by  this  machine  it  is  necessary  that  it  should  be 


Air 


Exhaust 
Discharge 


FIG,  53. — Turbine  with  exhaust  under  reduced  pressure  without  regenerator. 

operated  at  a  constant  temperature,  and  it  is  desirable  that 
the  temperature  of  the  exhaust  gases  should  be  brought 
down  to  300°  C.  absolute,  before  these  gases  enter  the  suction 
blower,  because  the  work  absorbed  by  the  machine,  R  T\og  (/), 
is  proportional  to  the  absolute  temperature  of  the  gases. 

This  result  may  be  obtained  by  cooling  the  gases  by 
means  of  an  abundant  injection  of  water,  in  connection 
with  the  use  of  a  sort  of  barometric  condenser  ( Fig.  53), 
or  by  the  use  of  a  tubular  refrigerator  with  circulating 
water  (Fig.  54). 


140 


THE   GAS   TURBINE. 


It  is  evident  that  this  latter  method  may  be  used  in  con- 
nection with  some  system  of  regeneration.  The  gases  may 
also  be  cooled  in  the  vaporizer  of  sulphurous-acid  gas, 
forming  part  of  a  refrigerating  machine,  as  we  shall  see  here- 
after (Fig.  55). 


Water 

FIG.  54. — Turbine  with  exhaust  under  reduced  pressure,  without  regenerator,  with  inter- 
cooler. 


s& 

^ 

Turbine 

1 

LJ 

Exhauster                      Turbine 

/" 

^ 

•—^SOz  Liquid 

«,  S02  Gas 

Gases 

FIG.  55. — Turbine  with  exhaust  at  reduced  pressure,  with  recovery  of  waste  heat  by  a 
sulphur  dioxide  turbine. 

The  system  of  exhausting  at  low  pressure  enables  a 
regenerator  to  be  employed,  but  the  construction  of  the 
regenerator  is  not  very  easy,  because  the  transmission  of 
heat  is  not  very  active  at  low  pressures. 

There  are  three  methods  in  which  the  system  may  be 
employed. 

The  temperature  of  the  exhaust  may  be  brought  below 
700  degrees  by  the  use  of  some  one  of  the  cycles  already  dis- 
cussed, this  plan  permitting  the  use  of  a  multistage  turbine, 


THE   GAS   TURBINE.  141 

although  at  the  expense  of  a  certain  increase  in  the  work 
of  compression.  The  actual  balance  of  power  can  only  be 
definitely  determined  by  examining  each  case  by  itself. 
Still  we  have  already  seen,  that,  in  general,  if  we  attempt 
to  increase  the  efficiency  y  by  the  use  of  a  multistage  tur- 
bine, the  total  effect  will  be  improved  to  a  greater  extent 
if  we  increase  the  amount  of  heat  supplied  rather  than  by 
lowering  the  temperature  of  the  exhaust. 

The  second  application  of  the  system  which  we  are  con- 
sidering consists  in  increasing  the  expansion  ratio,  and 
utilizing  this  increase  to  allow  a  corresponding  increase  in 
the  amount  of  heat  supplied,  while  maintaining  the  tempera- 
ture of  the  exhaust  at  700  degrees.  This  method  presents 
especial  advantages  in  cases  in  which  the  efficiency  is  limited 
by  consideration  of  the  maximum  pressure  of  the  cycle; 
which  is  notably  true  in  the  explosion  cycles. 

Finally,  we  may  utilize  the  low-pressure  exhaust  in  a 
manner  which  avoids  the  use  of  a  piston  compressor.  We 
shall  see  that  multicellular  turbine  compressors  are  not  well 
adapted  for  the  production  of  very  high  pressures.  Under 
such  conditions  their  efficiency  is  materially  reduced  by 
reason  of  the  friction  of  the  latter  wheels  of  the  series 
in  the  gas  or  air  of  high  density.  It  is  therefore  better  to 
arrange  a  turbine  compressor  to  deliver  the  gas  into  the 
combustion  chamber  at  a  pressure,  say,  of  six  atmospheres, 
and  follow  the  gas  turbine  by  an  exhaust  blower,  reducing 
the  exhaust  pressure  to  J  atmosphere,  than  it  is  to  employ  a 
single  compressor  operating  at  a  pressure  of  36  atmospheres. 

In  addition,  the  power  turbine  will  operate  with  less 
frictional  resistance  by  reason  of  the  lower  pressure. 

It  seems  as  if  some  such  arrangement  as  this  is  necessary 
if  the  piston  compressor  is  to  be  entirely  eliminated  in  gas 
turbine  design. 

From  a  thermodynamic  point  of  view  there  should  be 
no  difference  between  the  operation  with  exhaust  at  low 


142 


THE   GAS   TURBINE. 


pressure  or  at  atmospheric  pressure,  provided  the  ratio  of 
the  two  extreme  pressures  is  the  same  in  both  cases;  and 
provided  that  the  two  compressors  operate  isothermically 
and  at  the  same  temperature  T0,  in  both  cases. 

III. 
Cycles  Using  Heat  Regenerators. 

It  is  understood  that  it  is  possible  to  employ  cycles 
having  the  same  efficiency  as  that  of  Carnot  between  the 
same  limits  of  temperature,  by  replacing  the  adiabatics  of 
the  Carnot  cycle  by  two  isodiabatics.  The  two  simplest 
solutions  of  this  problem  are  those  of  Stirling  and  of  Erics- 
son, but  the  first  of  these  involves  reheating  under  constant 
volume,  and  is  not  applicable  to  our  case. 

The  Ericsson  Cycle. 

In  the  Ericsson  cycle,  on  the  contrary,  the  exchanges 
of  heat  are  made  under  constant  pressure:  the  two  isodia- 
batics are  isobarics. 


A  fo 


FIG.  56. — Ericsson  cycle. 

The  gas  is  compressed  along  AB  at  the  constant  tempera- 
ture T0m,  it  is  reheated  under  constant  pressure  (p^  along 
BCj  by  means  of  a  regenerator,  which  raises  the  tempera- 
ture to  T2.  The  heat  furnished  by  the  fuel  is  introduced 


THE   GAS   TURBINE.  143 

along  CD  at  the  constant  temperature  T2,  during  which 
the  pressure  falls  to  p0.  Finally  the  gas  is  cooled  in  the 
regenerator,  from  T2  to  T0,  at  the  constant  pressure  p0. 

Unfortunately  this  cycle  cannot  be  realized  in  practice 
any  more  than  can  the  Carnot  cycle. 

Independently  of  the  practical  difficulty  of  obtaining 
an  isothermal  combustion  in  the  expansion  nozzle,  we  en- 
counter the  impossibility  of  introducing  large  quantities 
of  heat  without  using  excessively  high  compressions,  for 
we  have: 

Pi  =  eARJr2 
Po 

T 
The  thermal  efficiency  p  =  l — TTT  cannot  exceed  0.57, 

*  2 

since  the  gases  are  discharged  upon  the  turbine  wheel  at  a 
temperature  T2. 

The  work  of  compression  "TTc  is  given  by: 

Urologhyp(f)     or    RT.-^r 

\PQ/  A-tt  1  3 


, 
whence 


We  then  have          ,0  =  0.57     and  =  0.75 

(ju 

also  )?=0.15     and     ^^=0.15X0.57=0.086 

We  see,  therefore,  that  the  Ericsson  cycle  is  neither 
practicable  nor  advantageous.  It  is  possible,  however,  to 
apply  the  principle  of  regeneration  to  other  cycles,  and  as 
we  shall  see,  with  advantageous  results. 

In  general,  the  method  of  regeneration  is  available  only 
for  cycles  using  isothermal  compression,  and  especially  those 
in  which  the  combustion  takes  place  under  constant  pressure. 


144 


THE   GAS   TURBINE. 


Cycles  Employing  Isobaric  Introduction  of  Heat. 

As  large  a  proportion  as  possible  of  the  heat  contained 
in  the  exhaust  gases  should  be  recovered  by  passing  these 
hot  gases  through  a  system  of  tubes  by  means  of  which 
they  heat  the  compressed  gas  on  its  way  to  the  combustion 
chamber.  We  see  that  with  a  regenerating  surface  of 
infinitely  great  extent  we  might  recover  all  the  heat,  if  the 
compressed  gas  to  be  heated  left  the  compressor  at  the  ordi- 
nary temperature  (say  about  300°  C.  absolute).  This 
involves  an  isothermal  compression,  while  if  the  compres- 
sion is  adiabatic  the  exhaust  gases  cannot  be  cooled  below 
the  final  temperature  of  compression. 


O  V 

FIG.  57. — Cycle  with  isobaric  combustion  and  isothermal  compression. 

The  compression  is  accompanied  by  a  consumption  of 
heat: 


We  then  introduce  by  regeneration  K  calories  under 
the  constant  pressure  piy  and  the  temperature  passes  from 
T0  to  TV  We  have 

K  =  CP(T,-T.}. 

The  fuel,  furnishing  Q  calories,  raises  the  temperature 
from  T1  to  T2: 


THE   GAS   TURBINE. 145 

The  adiabatic  expansion  from  p^T2  to  p0T3  gives: 

y-l 


If  the  regeneration  could  be  complete  the  gas  would 
enter  the  regenerator  at  T3  and  leave  it  at  T0,  the  surround- 
ing temperature,  leaving  behind  it  CP(T3  —  T0)  calories. 
But  in  reality  the  temperature  of  the  gases  is  not  reduced 
to  T0,  besides  which  the  compressed  gas  cannot  acquire  all 
the  heat  units  thus  gathered,  because  of  the  losses  by  radi- 
ation, conductivity,  etc.  If  we  call  the  total  efficiency  of 
the  operation  //,  we  have  : 


For  example,  if  the  gases  leave  the  turbine  at  700  degrees 
they  contain  92  calories  per  kilogramme  which  are  recover- 
able, and  we  have  K  =92  /*. 

Here  the  quantity  of  heat  introduced  in  the  cycle  is 
(K  +  Q),  the  quantity  given  up  in  cooling  during  the  com- 
pression is  Q'  ',  and  that  which  is  discharged  with  the  exhaust 
is  equal  to 


The  quantity  of  heat  converted  into  useful  work  is  there- 

fore equal  to: 

(K+Q)-Q'-CP(T3-T0). 

The  actual  amount  of  heat  abstracted  from  the  fuel 
being  Q,  we  then  have: 

(K+Q)-Q'-CP(T,-Ta) 

p=         nr 

If  we  maintain  a  standard  temperature  of  the  exhaust, 
say  700°  C.  absolute,  the  value  (K+Q)  of  the  total  heat 
introduced  is'  equal,  for  each  compression  ratio,  to  that 
which  has  been  computed  for  cycles  without  regeneration. 
It  follows  that  the  useful  work  obtained  per  kilogramme  of  air 

10 


146 


THE   GAS   TURBINE. 


is*s  1  1 


OOOO  OO 

'^^fr^     t^-cocoo  "^ 

'iSlii     coi>-i>-oo  co 

dddd  dddd 


§      8«? 

H    CO 


$ 


d     d 


coo 
ioco 


oooo 


d     d 


THi-IOD       COO-^QO       232^S? 

^^^  §sss  sill 


w  d  o 


II 

OTM 


0000 


dd 


• 

i—  ico 


33 


O 


Ils3  1 


1 


dddd 


oooo 


dddd 


° 


s\+  8 

H^ 


Temperature  of  combusti 
Total  introduction  of  hea 


il 

O      02 


OiCM       OCOO5(N 
COOS  Tt^COOi 


Si58  8S£8  8SJ28 

o'drH  dddr-5  dodi-H 

II   II   II  II   II   II   11  II   II   I!   II 

5L^^-  =t    5J_    5L    =L  =L    «.    =L    «. 


I 

i  3 
5.1 

** 


A 
A 

f 


Equivalent 
Equivalent 


Ratio  =- 


echanical  efficiency 


r-* 


1 


•1  S. 
1.* 

<D     .. 

S.b 

-s  * 
S-s 

15  o 

"! 

cs  a 


Eq 
Co 


THE   GAS   TURBINE. 


147 


is  not  increased  by  the  use  of  the  regenerator,  and  the  ratio 
of  the  work  of  compression  to  the  useful  work  is  not  changed. 
The  table  on  page  146  gives  the  results  for  various  ratios 
of  compression,  and  for  an  exhaust  temperature  of  700°  G. 
absolute.  'i 


FIG.  58. — Cycles  with  isothermal  compression  and  isobaric  combustion  with  regenerator. 

Exhaust  at  700°  C. 

The  principal  advantage  of  the  regenerator  is  that1  it 
permits  the  attainment  of  the  same  total  useful  effect  with 
much  lower  compression  ratios.  Thus,  when  the  coefficient 
of  regeneration,  /*,  reaches  0.75  a  total  useful  effect  of  0.30 
is  secured  with  a  compression  ratio  of  25,  while  without 
regeneration  a  compression  of  60  would  be  required  to  secure 
the  same  efficiency. 


148  THE   GAS   TURBINE. 

For  a  given  compression,  a  regeneration  of  50  per  cent. 
(/*  =  0.5)  improves  the  total  useful  effect  py  from  10  to  30  per 
cent,  and  a  regeneration  of  75  per  cent,  improves  the  total 
useful  effect  from  15  to  30  per  cent.,  according  to  the  com- 
pression; the  influence  of  the  regenerator  being  greater  with 
low  compressions  than  with  the  higher  compression  ratios. 

The  use  of  the  regenerator  does  not  extend  the  limit  of 
maximum  total  useful  effect  except  when  the  compression 
ratio  exceeds  80.  In  this  case  we  are  limited  by  the  calorific 
value  of  the  fuels,  which  control  the  maximum  amount  of 
heat  introduced.  The  use  of  the  regenerator  permits  this 
maximum  to  be  extended. 

Summing  up,  with  a  coefficient  of  regeneration  of  0.75, 
which  seems  reasonable,  we  have  theoretically,  for  a  com- 
pression ratio  of  25,  the  possibility  of  obtaining  an  effective 
horse-power  hour  with  2100  calories;  and  writh  a  compres- 
sion ratio  of  60  we  may  produce  a  horse-power  hour  with 
about  1800  calories.  These  are  very  encouraging  results. 

The  following  table  (page  149)  gives  the  quantity  of 
heat  transmitted  to  the  regenerator  to  obtain  a  given 
amount  of  available  mechanical  work. 

It  is  seen  that  high  compressions  have  the  advantage 
of  reducing,  to  a  large  degree,  the  quantity  of  heat  to  be 
regenerated.  Thus,  with  a  value  /*=0.75  it  is  necessary  to 
transmit  to  the  regenerator  510  calories  per  net  effective 
horse-power  if  the  compression  ratio  is  25,  and  only  290 
calories  if  the  compression  ratio  is  60. 

The  transmission  of  heat  per  effective  horse-power  in 
the  condensers  of  steam  engines  ranges  from  3180  to  6360 
calories  per  horse-power  hour,  according  as  the  engine  con- 
sumes 5  or  10  kilogrammes  of  steam  per  horse-power,  while 
the  condensing  surface  ranges  from  0.10  to  0.30  square 
metre  per  horse-power. 

The  exhaust  gases  of  the  turbine  enter  the  regenerator 
at  a  temperature  of  700°  C.  absolute,  and  should  leave  it  at 


THE   GAS   TURBINE. 


149 


£ 


*  I 


-ft  -ft  -ft  -ft  -ft  -ft 

II     II     II       II     II  II 

i-1  P  P  H-1  O  O 

8  S  S  8  a  S 


CO        tO        H-1 

00*      OS       £ 


I"1     p     p 

CO       CO       OS 

to      co      os 


o 
to 


pop 

bo     bs     '^ 
o     o     o 


(-»        H-        O 

bi    M  ^ 

*-      OS      —I 


o     o    o 


H-»        p        O, 

8   8   g 


h-»    p    p 

o    bo     en 

OO        I— '       rf^ 


pop 

rf^       OO       tO 
OO       Oi       rf^- 


pop 

CO      -<l      4^- 

OS       to       00 


O      O       P 

4^       io       to 
CO       CO       £1 


P       P 
^       OS 

CO      O 


oo 


pop 

*<$$  ^r  CO 


pop 

CO       tO       J-J 

o     co     en 


pop 
en  4^.  to 
Co  <o  **-J 


O       O      O 


000 


pop 

rf^       OO       tO 


$50  _  THE   GAS   TURBINE.  _ 

400°  absolute  to  realize  a  regenerative  efficiency  of  75  per 
cent.  The  compressed  air  enters  at  300°  and  leaves  at  600°. 
With  a  systematic  circulation  the  drop  in  temperature  will 
be  100°  from  the  entrance  to  the  exit,  and  the  mean  tempera- 
ture drop 

D-d 


log 

is  thus  100  degrees. 

We  find  in  steam  superheaters  a  heat  transmission  of  10 
to  15  calories  per  hour,  per  square  metre,  per  degree,  or  in 
the  present  case,  1000  to  1500  calories. 
We  then  have: 

510 
1000  to  1500 

square  metres,  or 


0.34  to  0.51 


=  0.20  to  1.30 


1000  to  1500 

square  metres  per  net  effective  horse-power. 

Thus,  to  realize  a  regenerative  efficiency  of  75  per  cent, 
with  a  compression  ratio  of  60,  it  will  suffice  to  have  about 
the  same  area  of  heat  transmitting  surface  as  would  be 
given  to  the  condenser  surface  for  a  steam  engine  of  the 
same  effective  power. 

Regeneration  in  Cycles  Using  the  Isopleric  Introduction 
of  Heat. 

This  case  may  be  treated  in  the  same  manner  as  the  pre- 
ceding. It  is  necessary,  however,  to  note  that  in  practice 
the  regenerated  heat  can  be  introduced  only  at  constant 
pressure  and  does  not  act  to  raise  the  final  pressure.  The 
latter  will,  therefore,  not  be  so  high  for  a  given  initial  com- 
pression as  in  cases  in  which  there  is  no  regeneration, 
and  this  diminishes  somewhat  the  advantages  of  the  explo- 
sion cycle. 


THE   GAS   TURBINE. 


151 


The  following  results  are  deduced  from  the  computation: 


Q 


1— i 


which  give  for 
ing  table. 


=  0.5  and  T3  =700°  the  results  in  the  follow- 


Compression ratio  — 

5 

10 

is 

20 

T6mp6ra.tu.r6  of  explosion  T>,     

1540 

2030 

2380 

2680 

16 

41 

73 

110 

Heat  furnished  by  combustible  Q 

177 

260 

319 

370 

Thermal  efficiency  p  «         

0.55 

0.64 

0.68 

0.71 

Eouivalent  A  ""GYt  of  useful  work                        .... 

98 

166 

217 

262 

Ratio  ^ 

033 

029 

0.26 

0.24 

°  ^u  '  ' 
IVlechanical  efficiency  f]                              ... 

046 

049 

0.51 

0.53 

Total  useful  effect  py 

025 

031 

035 

038 

Equivalent  Arj^u  of  net  mechanical  work  TJ^U  .  . 
Consumption  of  air  kg  per  H  P  hour  eff 

45 
14  10 

81 
790 

111 
5  70 

139 

460 

Ratio  of  calories  regenerated  to  effective  work  .  .  . 

1.00 

0.57 

0.42 

0.33 

We  thus  obtain  the  same  results  as  with  combustion  at 
constant  pressure,  but  with  compressions  only  about  one- 
half  as  great.  The  absolute  maximum  of  useful  effect  is  not 
increased,  since  we  are  limited  by  the  consideration  of  the 
pressure  and  temperature  of  explosion  to  compression 
ratios  only  about  one-half  as  great. 

IV. 

Cycles  Involving  the  Injection  of  Water,  Steam, 
or  Cool  Gases. 

We  have  already  seen  that  it  is  very  desirable  to  be  able 
to  reduce  the  amount  of  gas  to  be  compressed  to  realize  a 
given  amount  of  work.  If,  to  fix  our  ideas  upon  this  matter, 
we  assume  compression  ratios  above  80  to  be  excessive,  we 
cannot  introduce  more  than  450  calories  per  kilogramme  of 


152  THE   GAS   TURBINE. 

gas,  while  there  are  certain  combustible  mixtures  which 
readily  furnish  from  550  to  600  calories.  We  are  therefore 
obliged  to  dilute  these  latter,  and  thus  increase  the  volume 
of  gas  to  be  compressed  some  20  to  30  per  cent.  This  incon- 
venience becomes  aggravated  with  lower  compressions. 

This  fact  has  led  to  investigations  as  to  whether  we  may 
not  use  the  rich  combustible  mixtures  without  dilution  by 
using  certain  artifices  to  limit  either  the  temperature  of 
combustion  or  the  terminal  temperature. 

Limitations  of  the  Temperature  of  Combustion. 

The  external  cooling  of  the  combustion  chamber  is  en- 
tirely inconvenient.  The  calories  thus  abstracted  take  no  part 
in  the  development  of  power.  It  would  be  simpler  and  more 
economical  to  reduce  the  amount  of  combustible  introduced. 


^To  steam 


\v 

>*-Water  injected 
FIG.  59. — Combustion  chamber  for  gas  and  steam  turbines. 

But,  if  the  heat  abstracted  can  be  used  to  vaporize  water, 
and  if  the  steam  thus  produced  is  delivered,  either  to  a 
separate  turbine;  or,  by  a  separate  nozzle,  to  the  main  gas 
turbine;  or  into  the  expansion  nozzle  of  the  gas;  or,  finally, 
into  the  combustion  chamber  itself,  this  heat  will  partake 
in  the  development  of  power  according  to  a  cycle  more  or 
less  effective,  and  the  loss  will  be  reduced. 


_      THE   GAS   TURBINE.  _  153 

Suppose,  for  instance,  that  the  steam  thus  produced 
is  utilized  in  a  separate  turbine,  which  may  be  either  con- 
nected to  a  condenser  or  exhaust  into  the  atmosphere. 
The  combustion  chamber  of  the  gas  turbine  will  then  act 
as  the  furnace  of  the  steam  boiler  for  the  separate  turbine. 
Leaving  aside,  for  the  moment,  the  complication  of  this 
arrangement,  and  assuming  that  we  vaporize  the  water 
in  the  generator  to  a  pressure  of  20  atmospheres  and  super- 
heat the  steam  to  a  temperature  of  700  degrees  absolute, 
by  means  of  the  calories  derived  from  the  walls  of  the  com- 
bustion chamber  we  obtain  a  temperature  of  ebullition  of 
488  degrees  absolute. 

The  heat  contained  in  a  kilogramme  of  water  will  be: 

calories. 


If  the  exhaust  is  discharged  into  the  air,  the  temperature 
will  be  373°  absolute,  while  if  a  condenser  is  used  the  tem- 
perature will  be  about  320°. 

The  thermal  efficiency  of  the  steam  portion  of  the  system 
wilF  be: 

Exhausting  into  atmosphere: 


_  ^700  -  ^73  _  843  -  637 
~  " 


843 

^=0.172 

Exhausting  into  a  condenser: 


-700 

^  =  0.185. 

In  steam  turbines  the  mechanical  efficiency  y  is  about 
0.70.  The  result  obtained  when  operated  with  a  condenser 
corresponds  to  a  consumption  of  steam  of  about  4  kilo- 
grammes per  effective  horse-power  (8.8  pounds).  Now  a  gas 
turbine,  without  regeneration  or  water  injection  and  with  a 
compression  ratio  of  10,  gives  a  total  efficiency  ^=0.18. 


154 


THE   GAS  TURBINE. 


The  arrangement  which  we  have  been  discussing  is 
therefore  without  interest  as  regards  efficiency  unless  we 
adopt  compressions  higher  than  10.  The  only  advantage 
lies  in  the  reduction  in  the  importance  of  the  compressor. 

If  the  steam,  produced  at  the  expense  of  the  heat  devel- 
oped in  the  combustion  chamber,  is  delivered  upon  the 
wheel  of  the  gas  turbine  through  separate  nozzles,  the  effici- 
ency will  be  the  same  as  above,  and  the  same  conclusions 


Combustible 


To  the  ? 
turbine 


injected 
FIG.  60. — Combustion  chamber  for  mixed  turbine  taking  steam  from  jacket. 


Water  injected 
Combustible 


FIG.  61. — Combustion  chamber  for  mixed  turbine  with  independent  water  injection. 

follow.  The  same  is  true  if  the  steam  is  mingled  with  the 
burned  gases  in  the  expansion  nozzles  of  the  gas  turbine 
itself;  and  with  this  arrangement  certain  precautions,  im- 
portant from  a  kinetic  point  of  view,  are  necessary,  as  will 
be  seen  hereafter. 

Finally,  if  the  steam  produced  at  the  expense  of  the  heat 
in  the  combustion  chamber  is  delivered  into  the  combustion 
chamber  itself,  the  result  will  be  the  same  as  if  the  water 
were  delivered  directly  into  the  combustion  chamber  in 


THE   GAS   TURBINE.  155 

the  liquid  form.     This  is  the  arrangement  which  we  shall 
now  examine  (Fig.  60). 

Let  x  be  the  weight  of  water  injected  per  kilogramme 
of  gas  burned,  and  let  p  be  the  pressure  in  the  combustion 
chamber.  The  tension  pl  of  the  steam  is  found  from  the 
law  of  the  mixture  of  gases  and  vapors,  and  is  equal  to : 

P  ~ 


in  which  R  and  Rl  are  the  specific  constants  of  air  and  of 
the  vapor  of  water.    Supplying  these  constants,  we  have: 

i=  46.8  a; 

P  ~P29.3+46.8z* 

Let  6  be  the  temperature  of  ebullition  which  corresponds 
to  this  pressure  p1. 

The  heat  absorbed  by  the  vaporization  of  1  kilogramme 
of  water  injected  at  0°,  into  the  combustion  chamber,  is 
given  by: 

A«=g+r=606.5+0.305(0-273). 

The  steam  produced  is  also  superheated,  and  if  we 
represent  the  mean  value  of  the  specific  heat  of  this  steam, 
superheated  between  the  temperatures  of  6  and  772,  by  Cp&^21 
the  superheating  will  absorb 

CpoT2(T2—6)  calories. 

The  total  amount  of  heat  absorbed  by  1  kilogramme 
of  steam  may  readily  be  calculated  by  assuming  0.48  as  the 
mean  value  of  the  specific  heat  of  steam,  and  by  using  the 
formula  of  Lorenz 


which  gives: 


/T 
\a 


with  a  =  0.43     and     b  =  36Xl05. 


156 


THE   GAS   TURBINE. 


; 


If  we  take  the  value  of  7-  the  same  for  the  superheated 
steam  as  for  the  gas,  we  may  calculate  the  temperature  at 
the  end  of  the  expansion  Ts  and  the  corresponding  heat  of 
the  steam  XTz,  from  whence  the  thermal  efficiency  p  of  the 
steam,  considered  separately,  will  be: 


It  will  be  observed  that  XT2  and  XTz  are  dependent  upon 
the  ratio  x,  or  the  proportion  of  water  to  gas,  by  weight. 
The  lower  this  ratio  is  the  more  the  tension  of  the  steam  is 
reduced  with  relation  to  the  pressure  of  combustion  p.  If 
the  computations  are  made  it  will  be  found  that  the  results 
differ  very  little  from  those  corresponding  to  the  case  of 
saturated  steam  without  the  presence  of  any  air  (in  which 
x  =  infinity)  at  least  when  the  temperatures  are  relatively 
high,  as  in  the  case  which  we  are  considering. 

The  following  table  gives  the  results: 


Absolute  pressure  of  combustion  p 

s 

10 

15 

20 

25 

30 

40 

Temperature  of  combustion  T2      

1120 

1305 

1533 

1680 

1780 

1880 

2050 

Temperature  of  ebullition  0 

425 

453 

472 

488 

498 

503 

523 

Heat  of  vapor  Aj^  

990 

1130 

1230 

1310 

1390 

1490 

1580 

Heat  of  vapor  Ay3  .  .  .  . 

790 

790 

790 

790 

790 

790 

790 

<  for  the  vapor  .  . 
Thermal  efficiency  p  .  <  ,     A. 
1  for  the  gas  

(  for  the  vapor  .  . 
Total  efficiency  ?/>...  <  ,      ., 
1  for  the  gas  

0.20 
0.34 
0.14 
0.11 

0.30 
0.43 
0.21 
0.16 

0.36 
0.47 
0.25 

0.18 

0.40 
0.52 
0.28 
0.22 

0.43 
0.55 
0.30 
0.25 

0.47 
0.57 
0.33 
0.26 

0.50 
0.60 
0.35 
0.28 

This  table  is  computed  on  the  assumption  that  x  =  in- 
finity, T3  =  700°  absolute,  and  that  the  exhaust  is  discharged 
against  atmospheric  pressure.  If  the  exhaust  pressure  is 
reduced  the  figures  will  be  modified. 

It  will  be  seen  that  the  thermal  efficiency  of  the  cycle 
of  the  vapor  is  lower  than  that  for  the  gas,  but  if  we  consider 
the  total  efficiency  T^O,  taking  the  efficiency  of  the  turbine 


THE   GAS   TURBINE. 157 

at  0.7,  and  that  of  the  compressor  (including  its  transmis- 
sion) also  at  0.7,  these  results  are  reversed.  This  follows 
because  the  work  of  the  compressor  is  reduced  by  the  use 
of  the  steam. 

We  conclude  from  this  analysis,  that  the  injection  of 
water  is  more  advantageous  than  the  introduction  of  an 
excess  of  air  for  combustion,  above  all  because  it  permits 
a  material  reduction  in  the  dimensions  of  the  compressor. 

It  may  be  desirable  to  consider  whether  or  not  there  is 
any  risk  of  the  dissociation  of  the  water  under  the  conditions 
of  temperature  and  pressure  existing  in  the  combustion 
chamber.  In  all  probability  there  is  no  danger  of  such 
action,  since  dissociation  does  not  begin,  at  atmospheric 
pressure,  until  a  temperature  of  1300  degrees  C.  absolute, 
and  the  tension  of  dissociation  does  not  reach  a  value  of  0.5 
until  2100°  C.  At  the  pressures  under  consideration  there 
can  therefore  be  no  appreciable  dissociation,  and  there  can 
be  still  less  during  the  expansion,  for  the  drop  in  tempera- 
ture with  the  pressure  is  very  rapid. 

Injection  into  the  Combustion  Chamber,  of  Steam 
Produced  in  a  Regenerator. 

It  has  been  proposed  to  replace  the  introduction  of  an 
excess  of  air  in  the  combustion  chamber  by  an  injection 
of  steam.  If  this  steam  is  produced  by  the  combustion  of 
fuel  under  a  boiler  the  result  will  be  the  same  as  in  the  case 
of  the  injection  of  water  which  we  have  just  examined. 
This  arrangement,  however,  would  be  accompanied  with 
the  heat  losses  involved  in  the  use  of  a  separate  boiler, 
together  with  the  mechanical  complications  accompanying 
it,  besides  which  it  would  be  necessary  to  inject  much  more 
steam  to  produce  the  same  effect. 

Assuming,  as  before,  that  x  =  infinity,  the  total  amount 
of  heat  absorbed  by  the  injection  of  a  given  weight  of  water 


158 


THE   GAS   TURBINE. 


in  the  liquid  state  is  1.5  to  2.5  times  greater  than  if  it  is 
injected  in  the  form  of  steam  at  6  degrees. 

The  injection  of  steam  into  the  combustion  chamber  is 
of  interest  only  when  the  steam  is  generated  in  some  form 
of  regenerator,  heated  by  the  exhaust  gases  of  the  turbine. 
We  will  examine  this  case,  always  assuming  that  the  pres- 
sure of  the  steam  in  the  mixture  is  the  same  as  that  of  the 
pressure  of  combustion. 

10 


10  20  30 

FIG.  62. — Efficiencies  for  mixed  turbines. 

The  exhaust  being  at  the  temperature  of  700  degrees 
absolute,  each  kilogramme  of  exhaust  gases  represents  92 
calories.  Each  kilogramme  of  water  carries  790  calories, 
but  only  153  calories  (the  sensible  heat)  can  be  regenerated 
without  condensation,  if  the  exhaust  takes  place  at  atmos- 
pheric pressure.  The  result  will  be  improved  if  the  exhaust 


THE   GAS   TURBINE.  159 

occurs  at  reduced  pressure,  and  if  we  take  into  account  the 
fact  that  the  pressure  of  the  vapor  is  lower  than  that  of 
the  surroundings  into  which  it  is  discharged. 

If,  then,  x  kilogrammes  of  water  are  mingled  with  1  kilo- 
gramme of  burnt  gases  we  may  regenerate  92  +  153x  calories, 
and  the  effective  recuperation  will  be  /*(92  +  153z),  which 
gives  a  vaporization  of  a  weight  of  water  x: 


92 


The  weight  of  steam  which  may  be  injected  is  thus  well 
denned  and  distinctly  limited.  If  6  is  the  temperature  of 
ebullition  corresponding  to  the  pressure  of  the  vapor  of 
water  in  the  mixture,  each  kilogramme  of  steam  injected  will 
absorb  a  quantity  of  heat  equal  to  CpoT-t  (^2  —  ^)-  This 
quantity  is  computed  below,  assuming  for  simplification 
that  6  is  equal  to  the  temperature  of  ebullition  at  the  pres- 
sure p  (page  160). 

The  injection  of  water  absorbing  ?  calories  per  kilo- 
gramme of  gas  burned,  it  is  possible  to  increase  the  amount 
of  heat  introduced  by  an  equal  amount  without  modifying 
the  temperatures  T2  and  T3,  provided  the  calorific  power 
of  the  combustible  will  permit  it. 

It  will  thus  be  found,  if  we  take  the  same  efficiency  for 
the  regenerator  (0.75,  for  example),  that  the  total  useful 
effect  obtained  differs  very  little  from  that  secured  by  the 
use  of  a  regenerator  heating  the  compressed  air.  Never- 
theless the  actual  consumption  of  air  per  effective  horse- 
power is  less,  a  fact  which  has  a  distinct  practical  advantage. 

This  method  is  especially  applicable  when  the  nature 
of  the  combustible  permits  the  introduction  of  a  large 
amount  of  heat,  and  when  the  exhaust  is  discharged  at  a 
reduced  pressure. 


160 


THE   GAS   TURBINE. 


3£§as?s 

•    T*    rH    1C    ^    rH 


O   O 


s  a 


s3s§ci|l 


§  » 

o     "* 


<M    X"    t- 

Qi     OO     QQ 


IP    rH    rH 


45 


CO    C<j    t>»        ^    OO 


§ 


^D    OO 
iC    <>l 

o  o 


^s^ilS 


8    - 

o     *"" 


8  S  S  a  »  a  «   •  ^  ^  ^ 

gs 33^8*3^23 


•    QO    S 
3^»     •w^     ^T1 


rH        01 


§    S    §    8 

3    «>    O    ^ 


^    01    W    ^    W    ^.    ^ 

0:1    rH    °°    °°    .-:    O    O 


O  rH 


cQoaoQoacntHcKQQ 

QlQ)Q)QjQ>Q>Q)Qj          .          .          .          . 

•C    g  'C  *C  'C  "C  'C  'C     •     •     •     • 

,OaOOOOQQ 

1  li  s  g"s 


S  6 


THE   GAS  TURBINE.  161 

The  regenerator  may  be  made  in  the  form  of  a  boiler 
similar  to  the  Serpollet  flash  boiler,  or  of  the  type  proposed 
by  Colonel  Renard. 

The  gases  enter  the  regenerator  at  a  temperature  of  700 
degrees,  and  leave  it  at  about  400  degrees  absolute.  The 
water,  raised  from  a  temperature  of  zero  to  450  or  500 
degrees  absolute,  will  be  vaporized  at  this  latter  tempera- 
ture, at  a  pressure  of  about  5.30  atmospheres.  It  is  easy 
to  compute  that  the  mean  drop  in  temperature  will  be  about 
100  degrees  in  the  boiler,  and  75  degrees  in  the  regenerator, 
corresponding  to  a  heat  transmission  of  3000  and  1500 
calories  respectively  per  square  metre  per  hour.  This  will 
require  about  0.0366  square  metre  of  surface  per  kilogramme 
of  air  consumed  per  hour  in  the  turbine,  or  about  0.16  square 
metre  per  horse-power  delivered  on  the  shaft,  the  consump- 
tion per  horse-power  hour  being  4.25  kilogrammes  of  air, 
and  0.51  kilogramme  of  water,  for  a  combustion  pressure 
of  30  atmospheres. 

The  necessary  heating  surface  will  therefore  be  of  the 
same  order  of  magnitude  as  that  of  the  condenser  of  an  ordi- 
nary marine  engine,  but  probably  greater  than  that  of  a  re- 
generator for  a  gas  turbine  using  a  regeneration  of  gas  to  gas. 

Practically,  vaporization  under  pressures  exceeding 
30  atmospheres  may  appear  to  offer  certain  difficulties. 
This  method  of  regeneration,  however,  becomes  very  simple 
if  the  exhaust  is  discharged  at  reduced  pressure.  The  pres- 
sure of  combustion,  for  example,  being  from  5  to  10  atmos- 
pheres, and  the  exhaust  pressure  |  atmosphere.  The  regen- 
erator-boiler should  be  operated  at  pressure  ranging  only 
from  5  to  10  atmospheres.  The  drop  in  temperature  would 
be  materially  increased,  which  would  facilitate  the  trans- 
mission of  heat.  At  the  same  time,  the  efficiency  of  the  cycle 
would  be  increased. 

Under  such  a  system,  using  a  producer  of  the  Gardie 
type,  operating  under  5  to  10  atmospheres  pressure,  the 

.  11 


162  THE   GAS   TURBINE. 

loss  of  the  sensible  heat  of  the  gas  could  be  avoided,  and 
the  proportion  of  steam  or  water  injected  increased. 

It  may  be  noted  that  in  the  case  of  compressors  using 
water  injection,  the  vapor  produced  from  the  injected 
water  is  evolved  with  the  gaseous  mass,  and  permits  an 
increase  in  the  amount  of  heat  introduced,  thus  improving 
the  efficiency. 

The  Use  of  Large  Injections  of  Water  in  Connection  with  a  Very 
Rich  Fuel.     Turbines  Using  Liquid  Oxygen. 

As  a  matter  of  curiosity  it  may  be  noted  that  if  pure 
oxygen  be  used  in  the  combustion,  the  total  weight  of  gas 
burned  would  be  only  about  one-fourth  that  otherwise 
required;  and  therefore,  the  introduction  of  heat  being 
quadrupled,  might  reach  2000  calories  per  kilogramme. 
The  injection  of  water  into  the  combustion  chamber  might 
then  be  materially  increased.  Such  a  mixed  turbine  would 
require  a  much  smaller  compressor,  consuming  much  less 
power,  or  if  liquid  oxygen  were  used  a  small  centrifugal 
pump  operating  at  high  pressure  would  replace  the  air 
compressor. 

A  machine  of  this  kind  would  require  three  such  pumps; 
one  for  the  liquid  oxygen,  one  for  the  liquid  fuel,  and  the 
third  for  the  water.  A  tubular  heater,  heated  by  the  exhaust 
gases,  would  heat  the  water  and  vaporize  the  liquid  oxygen, 
the  only  other  elements  required  being  the  combustion 
chamber  and  the  turbine  wheel. 

The  temperature  of  combustion  would  be  the  same  as 
before,  but  the  temperature  of  the  exhaust  would  be  materi- 
ally lowered  by  reason  of  the  calories  absorbed  by  the  vapor- 
ization of  the  oxygen,  so  that  the  thermal  efficiency  should 
be  at  least  equal  to  that  computed  above. 

With  regard  to  the  mechanical  efficiency  >?,  this,  neglect- 
ing the  work  absorbed  by  the  pumps,  would  be  above  0.70, 
because  of  the  absence  of  the  compressor.  The  total  useful 


THE   GAS   TURBINE.  163 

effect,  pi],  would  therefore  be  0.70  or  0.75  times  0.70,  or 
about  50  per  cent.  Although  the  amount  of  work  available 
would  thus  be  very  high,  the  velocity  of  discharge  of  the 
mixture  would  be  much  greater  than  in  the  ordinary  case, 
and  the  mechanical  efficiency  of  the  turbine  would  be  lower. 

Such  a  machine,  however,  would  be  extremely  light. 
It  is  true  that  it  would  be  necessary  to  carry  4  kilogrammes 
of  liquid  oxygen  and  5  kilogrammes  of  water  for  every  kilo- 
gramme of  petrol,  but  for  certain  applications  the  final 
result  would  be  very  favorable. 

While  this  application  of  the  gas  turbine  is  yet  within 
the  domain  of  scientific  curiosities,  it  is  by  no  means  an 
absurdity.  M.  Cailletet  has  not  hesitated  to  propose  a1 
similar  combination,  using  piston  engines,  for  the  design 
of  extremely  light  and  powerful  motors  for  aerial  or  sub- 
marine navigation. 

•  *  *  v 
Limitations  of  the  Temperature  of  Expansion.     Injection  of 

Water,  Steam,  or  Cool  Gases  after  Expansion. 

If  the  exterior  of  the  expansion  nozzle  is  cooled,  the 
expansion  is  no  longer  adiabatic*  and  cannot  be  subjected 
to  computation.  All  the  energy  thus  abstracted,  however,. 
is  evidently  lost. 

The  same  is  not  the  case  if  the  expanding  gases  are 
cooled  by  an  injection  of  water,  since  the  vapor  thus  formed 
is  added  to  the  fluid  mass.  Nevertheless,  at  a  temperature 
of  700  degrees,  and  at  atmospheric  pressure,  about  -^  of  the 
calories  absorbed  by  the  injection  are  lost  and  absorbed  by 
the  vaporization  properly  so-called. 

We  are  therefore  led  to  consider  the  injection  of  steam. 
If  the  velocity  of  the  steam  is  lower  than  that  of  the  current 
of  gases,  there  is  caused,  as  we  shall  see,  an  important  loss 
of  energy.  Let  us  then  assume  that  the  two  currents  have 
the  same  velocity.  In  order  to  accomplish  this,  it  is  neces- 
sary that  the  vapor  be  generated  at  a  pressure  higher  than 


164  THE   GAS   TURBINE. 

that  of  the  gas  in  the  combustion  chamber.  We  will  pass 
over  this  difficulty.  In  order  to  obtain  a  better  result  than 
is  secured  by  the  direct  injection  of  water  the  steam  must 
be  regenerated  by  the  use  of  waste  heat.  Under  these  con- 
ditions, and  assuming  that  the  expanded  steam  is  still 
saturated,  dry,  or  slightly  superheated,  and  calling  x  the 
weight  of  this  steam  delivered  for  each  kilogramme  of  air, 
calculated  as  heretofore,  we  may  complete  the  temperature 
7y  of  the  expanded  gas. 

Cp(ZY-700)  =  0.48(77-373)3 

167-180* 
whence  '*  -0.24-0.48z* 

We  may  then  calculate  the  new  temperature  of  combustion, 
the  new  introduction  of  heat,  and  the  new  efficiency: 


With  a  coefficient  of  regeneration  of  0.75  we  may  inject 
12  to  13  per  cent,  of  water,  and  permit  a  final  temperature 
of  expansion  of  the  gas  of  800  degrees  absolute  instead  of 
700°  C. 

It  is  thus  seen  that  for  a  given  compression  ratio,  the 
useful  effect  is  slightly  lower  than  that  obtained  by  injecting 
the  steam  before  the  expansion.  In  practice  the  injection 
of  steam  after  the  expansion,  offers  considerable  difficulties 
of  a  kinetic  order. 

We  will  now  consider  the  injection  of  cool  .gases. 

Injection  of  Cool  Gases  at  Low  Velocities. 

Stodola  has  shown  in  the  following  manner  that  a  mix- 
ture of  two  currents  of  gases  having  two  different  velocities 
V)i  and  w2  results  in  a  material  loss  of  kinetic  energy. 

There  are  two  cases  to  be  considered.  The  first  corre- 
sponds to  the  use  of  a  mixing  chamber  so  formed  as  to  per- 
mit the  operation  to  be  effected  without  raising  the  pressure. 


THE   GAS  TURBINE. 165 

The  second  case  corresponds  to  the  use  of  a  cylindrical 
chamber,  which  leads  to  an  elevation  in  the  final  pressure. 
If  we  call  dPx  the  force  acting  axially  upon  an  element 
dm,  and  call  77^  772,  and  n  =  IJl+II2  the  flow  by  weight,  the 
theorem  of  quantities  of  motion  gives: 


ndt       fn^dt        n2dt     \ 
— w  —  [  -l—Wi  H — —  w2 }  =  2dtdP3 
Q         \  Q  a 


g 

from  which  we  get: 


IJw=IIlw1 

This  is  the   formula  for  impact  of  non-elastic  bodies, 
and  the  loss  of  energy  is: 


_     1/77!    2     772     2\      1/7 
Z  =  -  -^  X  +—  2iu2  )  —  -s  — 
2\  2J     2 


w  . 
g  g 

If  we  call  ^3  and  0  the  respective  temperatures  of  the 
two  gaseous  currents  before  mixture,  and  T3'  the  tempera- 
ture after  mixture,  we  have: 

~  =  n2(T,' 

These  three  relations  enable  us  to  compute  the  tempera- 
tures and  the  efficiency. 

Let  us  take  the  extreme  case  in  which  the  gas  is 
injected  cold  and  without  velocity.  We  have  : 

w2  =  0;     and     w  =  -~w\ 

„   nji2  wf 

whence  -JT20* 

The  ratio  £  of  the  lost  energy  to  the  amount  of  energy 
available  in  the  gaseous  current  before  the  mixture  will  then 
be,  for  this  particular  case* 


For  example,  if  #2  =  1  kilogramme,  and  it  is  desired  to 
reduce  the  temperature  to   T'3  =  700  degrees  by  injecting 


166  THE   GAS   TURBINE. 

U2  kilogrammes  of  air  without  velocity  at  300  degrees  abso- 
lute (or  #=300),  the  limiting  case  corresponding  to  T3  =  T'3 

will  be  attained  when  -r  =  95  772. 

If  x  be  the  thermal  equivalent  of  the  kinetic  energy  of 
1  kilogramme  of  burned  gas  before  the  mixture,  we  have: 

-r=-ffXf  whence   jfx-=Q5U2,  and  U  =  ~—  1 
A     11  11  yo 

For  example, 

for                            /=100  200  300  400  calories 

we  have                772>0.05  1.10  2.15  3.20  calories 

and                          e>0.05  0.52  0.68  0.76  calories. 

There  is,  therefore,  a  considerable  loss  in  the  kinetic 
energy  of  the  gaseous  current  when  the  latter  attains  a  con- 
siderable value. 

Suppose  that  we  are  using  a  cylindrical  mixing  chamber. 
The  pressure  beyond  the  zone  of  mixture  will  then  be  higher 
than  that  in  front  of  it.  Professor  Stodola,  who  has  ex- 
amined this  question,  finds  that  there  may  be  two  solutions, 
and  that  the  velocity  of  the  mixture  may  have  two  distinct 
values.  One  of  these  corresponds  to  a  simple  mixture, 
with  a  loss  of  kinetic  energy  and  a  relatively  moderate  rise 
in  temperature.  The  other  corresponds  to  a  velocity  greater 
than  that  of  sound  and  involves  the  existence  of  a  shock 
of  compression  of  which  we  shall  speak  hereafter.  However 
the  mixture  may  be  effected  there  is  no  more  advantageous 
result  to  be  expected  than  in  the  preceding  case,  and  there 
is  nothing  to  be  deduced  from  the  idea  other  than  the  results 
involved  in  progressive  mixtures  in  successive  chambers. 

Injection  of  Cold  Gases  at  the  Same  Velocity  as  the 
Principal  Current. 

Suppose  now  that  the  cold  gases  are  given,  by  the 
use  of  a  blower  or  similar  apparatus,  a  velocity  equal  to 
that  of  the  principal  current,  and  that  the  mixing  chamber 
is  of  such  a  shape  that  there  is  no  increase  in  pressure.  In 
this  case  there  is  theoretically  no  loss  of  energy. 


THE   GAS   TURBINE.  167 

It  is,  however,  necessary  to  expend,  in  driving  the  blower, 
an  amount  of  energy  equal  to  the  necessary  kinetic  energy. 
The  question  then  presents  itself  as  follows:  Is  it  more 
advantageous  to  compress  all  the  air  required  and  deliver  it 
at  once  to  the  combustion  chamber,  or  to  compress  only  a  por- 
tion of  it  to  the  pressure  of  combustion,  and  to  cause  the  re- 
mainder to  be  delivered  by  a  blower  to  the  mixing  chamber? 

Let  us  suppose,  for  example,  that  we  have  a  combustible 
capable  of  permitting  an  introduction  of  about  520  calories 
per  kilogramme  of  mixture.  If  we  compress  to  10  kilo- 
grammes per  square  centimetre,  we  can  introduce  only  about 
260  calories  per  kilogramme  to  exhaust  at  700  degrees.  If 
we  do  introduce  520  calories  we  shall  have  a  temperature 
of  combustion  of  2500  degrees  and  an  exhaust  of  1270 
degrees.  The  kinetic  energy  will  be  equivalent  to  290 
calories  per  kilogramme  of  gas.  In  order  to  bring  the  tem- 
perature of  1270  to  700  it  will  be  necessary  to  mix  with 
each  kilogramme  of  burned  gases  1.32  kilogramme  of  air, 
and  the  kinetic  energy  to  be  imparted  to  this  cold  air  will 
be  equivalent  to  1.32x290=410  calories.  We  then  have 
at  the  outlet  of  the  mixing  chamber  a  kinetic  energy  equiva- 
lent to  290+410=700  calories  for  2.30  kilogrammes  of 
mixture.  We  will  get  in  work  on  the  shaft  0.7  X700  =490. 
Now,  the  work  required  for  the  compressor  will  be  48  calories 
and  for  the  blower  410,  a  total  of  458.  There  will  therefore 
each  have  to  give  an  efficiency  of  0.94  in  order  that  they 
should  not  absorb  more  power  than  the  turbine  itself  pro- 
duces. The  injection  of  cold  gases  is  therefore  wholly 
impracticable. 

V. 

Combination  Cycles.    The  Adaptation  of  a  Second 
Engine  to  Utilize  the  Waste  Heat. 

It  has  been  suggested  that  the  waste  heat  discharged 
by  a  gas  turbine  should  be  utilized  to  operate  a  second  tur- 
bine, employing  sulphurous  acid  gas,  for  instance,  or  even 
vapor  of  water.  We  have  already  shown  that  the  exhaust 


168  THE   GAS   TURBINE. 

gases  should  be  discharged  at  a  temperature  of  about  700 
degrees  C.,  absolute,  and  that  it  is  not  advantageous  to 
lower  this  temperature  by  diminishing  the  amount  of  heat 
introduced. 

The  heat  abstracted  from  the  gas  during  compression 
may  be  carried  off  by  water  circulating  about  the  compres- 
sion cylinders  and  through  the  inter-coolers.  The  amount 
of  heat  thus  withdrawn  compares  in  importance  with  that 
escaping  with  the  exhaust  gases,  but  its  temperature  is 
much  lower.  Theoretically,  the  temperature  of  the  jacket 
water  should  not  materially  exceed  that  of  the  atmosphere, 
and  in  no  case  should  it  be  higher  than  50  to  100  degrees  C. 
It  is  therefore  necessary  to  resort  to  some  substance  having 
a  low  boiling  point,  such  as  sulphurous  acid,  in  order  to 
utilize  this  heat  in  a  secondary  engine. 

We  have  at  our  disposal  from  150  to  200  calories  per 
kilogramme  of  gas  burned.  If  we  use  a  steam  turbine  as 
the  secondary  motor,  operating  at  a  pressure  of  20  kilo- 
grammes per  square  centimetre,  superheating  to  700  degrees 
absolute,  and  operating  condensing,  the  thermal  efficiency 
will  be: 


The  total  useful  effect  will  then  be: 
^=0.70X0.265  =  0.185. 

Now  if  the  vapor  of  water  had  been  used  directly  with 
the  gases  of  combustion  it  would  have  given  a  useful  effect 
of  about  0.30. 

It  has  been  proposed  to  replace  the  vapor  of  water  by 
a  gas  which  is  readily  liquefiable,  such  as  sulphurous  acid. 
According  to  Professor  Josse  an  indicated  horse-power  may 
be  obtained  in  the  secondary  motor  with  a  consumption 

*  This  result  agrees  with  practice,  since  it  corresponds  to  a  consumption 
of  4  kg.  (8.8  pounds)  of  steam  per  horse-power  hour,  and  consumptions  below 
4.6  kg.  have  already  been  obtained. 


THE   GAS   TURBINE. 169 

of  7800  calories,  or  even  with  5000  calories  when  operating 
at  a  pressure  of  25  atmospheres  (90  degrees  C.)  in  the 
condenser. 

This  last  figure  gives  a  thermal  efficiency  of  0.127,  or  a 
net  useful  effect  of  0.7  X0.127,  or  0.089. 

This  result  might  be  materially  improved  if  we  could 
permit  the  superheating  of  the  sulphurous  acid  gas  without 
causing  corrosion  upon  the  parts  of  the  turbine  with  which 
it  came  in  contact. 

In  any  case  a  secondary  turbine  would  permit  a  recupera- 
tion of  150  to  200  calories  X0.09  =  14  to  18  calories,  if  we 
use  sulphurous  acid,  or  92x0.185  =  17  calories,  if  we  use 
water,  admitting  a  coefficient  of  recuperation  /*  equal  to 
unity.  Taking  /i=0.75,  we  get  work  equal  to  about  13 
calories  per  kilogramme  of  gas.  Now  the  net  mechanical 
effort  y^u  realizable  per  kilogramme  of  gas,  with  or  without 
recuperation,  varies  between  25  calories  and  200  calories 
when  the  pressure  of  combustion  varies  from  5  to  100 
atmospheres. 

The  amount  of  work  recoverable  by  the  use  of  a  second- 
ary machine  is  therefore  not  of  sufficient  importance  to 
warrant  the  complication  of  a  separate  machine  to  secure  it.* 

VI. 

Conclusions  from  the  Thermodynamic  Study  of  the  Gas  Turbine. 

Method  of  Development  to  be  Adopted.    Probable  Efficiency. 

Probable  Divergence  Between  Theory  and  Practice. 

The  study  of  the  gas  turbine  from  a  thermodynamic 
point  of  view  does  not  appear  to  reveal  any  combination 
capable  of  giving  results  greatly  differing  from  those  already 
obtained  from  the  latest  improved  gas  engines.  The  high 
thermal  efficiencies  theoretically  probable  seem  to  be  offset 
by  the  low  mechanical  efficiency.  But  this  latter  is  capable 

*  In  practice  the  relative  importance  of  the  work  recovered  might  be  a 
little  greater,  since  all  losses  of  energy  have  the  effect  of  increasing  the  amount 
of  heat  in  the  exhaust  gases,  and  of  such  leaks  we  have  taken  no  account. 


170 


THE   GAS   TURBINE. 


of  improvement,  so  that  there  remains  a  margin  for  progress 
which  is  encouraging  for  the  future. 

The  analysis  which  we  have  undertaken  may  be  reviewed 
as  follows: 

1.  Combustion  under  constant  volume,  as  compared 
with  combustion  under  constant  pressure,  shows,  for  the 
same  initial  pressure,  a  better  efficiency,  while  at  the  same 


030 


0  1000  2000  8000 

FIG.  63. — Efficiencies  for  various  combustion  temperatures. 

time  it  permits  the  use  of  a  less  important  compressor. 
Nevertheless,  the  absolute  value  of  the  efficiency  is  not 
greater,  because  we  are  more  promptly  limited  by  the  maxi- 
mum limit  of  permissible  temperature  of  combustion  T2. 
This  is  true  either  for  the  specific  power,  or  for  the  consump- 
tion of  air  per  horse-power  hour. 


THE   GAS   TURBINE.  171 

This  method  is  advantageous,  therefore,  only  from  the 
point  of  view  of  the  necessary  compression  ratio.  This  is 
a  matter  for  consideration  if  we  limit  ourselves  to  the  use 
of  rotary  compressors.  In  practice  the  mechanical  efficiency 
is  low  because  of  the  kinetic  losses  due  to  irregularities  of 
flow  under  varying  operation,  besides  the  inconveniences 
attending  an  explosion  machine.  As  a  matter  of  fact,  the 
explosion  turbine  is  applicable  only  to  very  small  powers, 
and  for  machines  of  light  weight,  in  which  the  efficiency  is 
a  matter  of  secondary  importance,  and  preliminary  compres- 
sion is  undesirable. 

2.  Isothermal    combustion    involves    excessively    high 
ratios    of    compression,    and    is    otherwise    not    practically 
realizable. 

3.  It  follows  that  the  best  method  available  for  the  gas 
turbine   corresponds  to  that  for  the   gas   engine;   namely, 
combustion  under  constant   pressure,   with  a  preliminary 
isothermal  compression. 

4.  If  the  ratio  of  the  extremes  of  pressure  has  a  given 
value,  it  is  immaterial  whether  these  pressures  are  high  or 
low,  in  an  absolute  sense.     This  point  is  of  interest  in  con- 
nection with  the  question  of  exhausting  at  low  pressure, 
and  with  the  use  of  multiple  rotary  compressors. 

5.  The  temperature  of  the  exhaust  should  be  as  high 
as  practicable,  with  regard  to  the  maintenance  of  the  revolv- 
ing wheels.     It  is  deceptive  to  attempt  to  lower  it  by  pro- 
longing the  expansion  by  the  use  of  an  air  pump. 

6.  The  best  method  of  saving  the  heat  escaping  in  the 
exhaust  is  by  a  simple  tubular  regenerator  transferring  the 
heat  from  outgoing  to  incoming  gas.    Regeneration  by  means 
of  a  steam  boiler  is  worthy  of  consideration  only  for  very 
rich  combustibles,  and  the  best  plan  then  is  to  deliver  the 
steam  into  a  combustion  chamber. 

It  may  now  be  asked  what  important  relations  may  be 
established  practically  between  the  above  theoretical  deduc- 


172  THE   GAS   TURBINE. 

tions  and  the  practical  results  attainable  with  such  machines 
as  may  actually  be  constructed. 

It  is  probable  that  the  practical  cycles  will  differ  from 
the  theoretical  ones  in  the  gas  turbine  much  as  they  do  in 
the  gas  engine,  but  to  a  less  extent. 

Thus,  as  concerns  the  compression',  there  are  two  differ- 
ences between  theory  and  practice  in  effecting  isothernal 
compression.  One  is  the  increase  in  the  work  of  compression; 
the  other,  the  elevation  in  temperature  of  the  compressed 
gas,  reducing  the  value  of  Q,  and  consequently  the  specific 
power.  The  results  in  practice  lie  between  those  computed 
for  isothermal  compression  and  those  corresponding  to 
adiabatic  compression.  But,  as  we  have  seen,  the  difference 
is  not  very  great,  and  we  have  taken  a  sufficiently  low  value 
for  the  mechanical  efficiency  >?c  to  cover  any  discrepancy 
on  this  account. 

With  respect  to  the  combustion,  there  are  more  import- 
ant divergences  between  theory  and  practice,  which  must 
be  taken  into  account.  Thus,  we  have  assumed  that  the 
reaction  is  effected  in  surroundings  wThich  are  strictly  adia- 
batic. This  cannot  be  effected  in  practice,  and  notwith- 
standing all  our  precautions  a  loss  of  heat  will  occur. 

The  combustion  will  also  be  incomplete,  hence  there  will 
be  a  loss  of  a  portion  of  the  combustible,  or  a  partial  dissocia- 
tion, this  being  less  probable  under  pressures  of  30  to  40 
atmospheres. 

These  three,  causes  have  one  and  the  same  result,  an 
increase  in  the  weight  of  combustible  consumed  per  horse- 
power hour.  This,  however,  does  not  affect  the  general 
development,  especially  if  the  fuel  is  in  the  liquid  or  solid 
state,  since  the  additional  amount  of  fuel  required  does  not 
affect  the  work  of  compression. 

The  specific  heat  of  the  products  of  combustion  differs 
materially  from  that  of  air,  and  varies  with  the  temperature; 
and  it  is  probable  that  the  value  taken  for  the  temperature 


THE   GAS   TURBINE.  173 

of  combustion  is  greater  than  the  real  value.  It  follows 
that  the  introduction  of  heat  is  more  limited  than  in  our 
-calculations,  at  least  in  the  case*  in  which  this  limit  is  fixed 
by  -the  calorific  value  of  the  combustible.  But  since  this 
limit  is  not  likely  to  be  reached  in  practice  the  only  effect 
resulting  from  the  disagreement  between  theory  and  prac- 
tice is  to  reduce  the  amount  of  air  required  for  dilution. 

Finally,  the  expansion  is  not  strictly  adiabatic,  and 
the  form  of  the  expansion  curve  is  not  precisely  that  which 
corresponds  to  the  relation 

pvl'4l  =  constant. 

Thus,  there  is  a  loss  of  heat  which  may  be  small,  but 
can  never  be  strictly  zero.  Besides,  the  gas  is  heated  to  a 
certain  extent  by  friction.  The  true  law  of  the  expansion 
can  be  determined  only  by  experiment.  In  any  case  the 
exponent  7  in  the  formula  will  differ  from  1.41  because  we 
are  dealing  with  gases  other  than  air  and  because  the  ratio 

C 
'-  is  not  constant   when  the  temperature  varies   between 

C 

very  wide  limits. 

Even  taking  into  account  the  variability  of  the  specific 
heats  with  the  temperatures,  M.  Vermand  has  shown  that 
the  law  of  Poisson  is  expressed  practically  by  the  relation: 

pvy  =  constant 

when  7-=i-f  — 

in  which  a  =0.162,  so  that  for  air  7- =  1.441. 

If  we  use  data  obtained  from  certain  trials  of  gas  engines, 
we  are  led  to  accept  for  7-  values  such  as  1.3  to  1.2. 

The  corresponding  results  differ  materially  from  those 
which  we  have  computed  above. 

Thus,  to  obtain  the  theoretical  temperature  of  700 
degrees  for  the  exhaust,  with  a  combustion  pressure  of  30 
atmospheres,  it  is  necessary  to  produce  a  combustion  tern- 


174 


THE   GAS   TURBINE. 


perature  of  1880  degrees,  introducing  375  calories  per  kilo- 
gramme of  air. 

These  are  the  results  obtained  above  for  7- =  1.4  (giving 
<o  =  0.57). 

If  now,  we  take  7-  =  1.3,  or  /--1.2  we  shall  have: 


snce  - 


'--=0.23  -=0.17 

r  r 

772=1526°  773  =  1253° 

9QK  /^) 9*30 

—  _-./*)  v^  —  ^Ov/ 

^?  =  0.45  ^  =  0.29. 

The  efficiency  is  influenced,  as  we  see,  to  a  remarkable 
extent  by  the  variation  of  7-;  and  the  diagram  (Fig.  64)  shows 


FIG.  64. — Variations  of  exponent  of  expansion. 

that  it  varies  almost  in  proportion  to  7- — 1,  at  least  in  the 
case  under  consideration,  in  which  the  cycle  uses  combus- 
tion at  constant  pressure  and  isothermal  compression.* 


*  The  thermal  efficiency  becomes  zero  for  >  =  1,  for  we  have  =*  =  (30)°=  1 
and  Q  then  becomes  zero.  ° 


THE   GAS  TURBINE. 175 

It  may  be  of  interest  to  note  the  following  values  for 

C 

F  =  -,  at  a  temperature  of  zero,  and  at  atmospheric   pres- 
c 

sure,  for  the  gases  named: 

H,0,N,  Air,  CO 1.41 

H2O 1.34 

CO2 1.29. 

In  engines  utilizing  the  explosion  of  gases  behind  a 
piston,  the  value  of  the  exponent  f  has  been  deduced  from 
the  form  of  the  expansion  curve,  and  the  figures  thus  ob- 
tained range  from  1.3  to  1.6.  In  such  machines,  however, 
the  action  of  the  walls  of  the  cylinder  play  an  important 
part,  while  in  the  diverging  nozzle  of  a  gas  turbine  this 
action  is  reduced  to  a  minimum,  because  a  continuous  flow 
is  maintained. 

However  this  may  be,  the  true  law  of  expansion  in  the 
nozzle  of  a  turbine  constitutes  the  principal  unknown 
practical  element  which  presents  itself  in  the  gas  turbine. 
It  has  even  been  maintained  that  7-  may  become  equal  to  1, 
and  that  the  expansion  may  be  accompanied  by  no  drop  in 
temperature,  and  hence  be  incapable  of  producing  any  use- 
ful effect.* 

Some  experimenters  have  not  been  able  to  find  the  drop 
in  temperature  by  thermometric  observations,  and  have 
attributed  this  fact  to  the  heat  developed  by  the  friction 
of  the  gases  upon  the  thermometer.  We  cannot  go  into  this 
objection  at  length.  The  expansion  doubtless  follows  the 
formula  of  Poisson,  pvy  =  constant,  but  the  true  value  of 
the  exponent  7-,  and  consequently  of  the  efficiency,  can  be 
determined  only  by  experiment. 

We  may  note  here  a  final  reason  for  the  discrepancies 
in  our  calculations  between  theory  and  practice.  This  is 

*  See  Charles  E.  Lucke,  Ph.D.,  Practical  Investigations  in  the  Gas 
Turbine  Problem;  Engineering  Magazine,  April,  1905.  The  Gas  Turbine, 
Engineering  Magazine,  August,  1906. 


176  THE   GAS   TURBINE. 

the  relative  inexactness  of  the  simple  physical  laws  which 
we  have  accepted  as  relating  to  the  substances  under  con- 
sideration: the  laws  of  Mariotte,  of  Gay  Lussac,  of  the 
constancy  of  specific  heats,  etc.  In  all  standard  works  there 
may  be  found  formulas  which  are  more  precise  than  those 
which  we  have  used,  and  these  may  be  substituted  for  the 
more  simple  laws.  The  greater  degree  of  precision  thus 
obtained  is  of  minor  interest,  since  the  inevitable  uncertain- 
ties of  the  question  render  any  such  excessive  precision 
illusory. 

Influence  of  the  Nature  of  the  Combustible. 

Before  leaving  the  thermodynamic  study  of  the  gas 
turbine  it  is  desirable  to  examine  whether  the  nature  of  the 
fuel  available  may  have  any  important  influence  upon  the 
possible  efficiency. 

In  order  to  use  the  most  advantageous  cycles  it  is  desira- 
ble, from  what  we  have  already  seen,  to  be  able  to  introduce 
from  375  to  415  calories,  if  we  do  not  inject  any  steam,  and 
from  470  to  524,  if  steam  injection  is  to  be  used;  the  pres- 
sure ranging  from  30  to  40  atmospheres. 

Now,  even  using  lean  gases,  such  as  that  made  in  the 
Dowson  producer,  or  the  waste  gases  from  blast  furnaces, 
with  a  heating  value  of  800  calories  per  cubic  metre  (about 
90  B.T.U.  per  cubic  foot),  it  is  possible  to  introduce  about 
460  calories  per  kilogramme  of  mixture;  while  with  the 
richer  gases,  such  as  illuminating  gas,  acetylene,  etc.,  we 
may  get  from  500  to  600  calories.  The  nature  of  the  com- 
bustible has,  therefore,  a  minor  influence  from  this  point 
of  view.  The  constitution  of  the  burned  gases  varies  but 
little  for  the  different  combustibles,  so  that  the  specific 
heats  are  not  greatly  different.  The  cycles  calculated  upon 
the  actual  composition  of  the  mixtures  will  therefore  agree 
fairly  well  with  those  which  we  have  based  upon  the  prop- 
erties of  air. 


THE   GAS   TURBINE.  177 

It  also  follows  that  the  total  weight  of  gas  to  be  com- 
pressed varies  but  little,  and  the  same  is  true  of  the  work 
required  for  compression.  When  a  liquid  fuel  is  used  a 
greater  amount  of  air  is  required  per  kilogramme  of  combus- 
tible than  with  a  gaseous  fuel. 

It  is  an  error  to  assume,  as  has  sometimes  been  done, 
that  gaseous  fuels  are  less  easily  employed  than  liquid  fuels. 
This  may  be  the  case  for  motors  of  the  Diesel  type  because 
the  intermittent  action  brings  in  the  important  question 
of  ignition.  Apart  from  the  necessity  for  two  separate 
compressors,  however,  the  compression  is  not  more  trouble- 
some when  a  gaseous  fuel  is  employed.  Since  the  combus- 
tion is  continuous  in  the  case  of  the  gas  turbine,  the  question 
of  ignition  is  of  secondary  importance. 

In  the  accompanying  table  the  computations  have  been 
made  according  to  the  stated  compositions  of  the  various 
gaseous  mixtures,  taking  the  data  calculated  by  M.  Vermand. 

It  will  be  seen  that  CP  varies  about  20  per  cent.,  and 
f  about  1  per  cent.,  in  passing  from  one  mixture  to  another. 

The  composition  of  the  burned  gases  varies  but  slightly. 
Nitrogen  predominates,  being  62  to  74  per  cent.,  followed 
by  carbon  dioxide,  12  to  33  per  cent.  Oxygen  appears  to 
be  present  in  very  small  quantities,  so  that  oxidation  of 
metallic  parts  need  hardly  be  feared. 

The  number  of  cubic  metres  of  air  and  of  gas  to  be  com- 
pressed to  correspond  to  the  introduction  of  an  amount 
of  heat  equal  to  100  calories  into  the  cycle,  gives  an  idea 
of  the  necessary  capacity  for  the  compressor,  or  compres- 
sors. As  this  quantity  varies  from  148  to  180  litres,  a  differ- 
ence of  22  per  cent.,  this  is  not  an  element  in  which  a  serious 
error  need  enter. 

In  like  manner  the  total  weight  of  gas  to  be  compressed 

per  100  calories  introduced  forms  a  measure  of  the  total 

power  required  for  the  compression.     The  extreme  limits 

are  0.17  and  0.22  kilogramme,  a  difference  of  30  per  cent. 

12 


178 


THE   GAS   TURBINE. 


s« 

Sa 

0) 

1! 

fcH 

I! 

a    CO     CO     O     rH         ' 

g  CN  co  ^  co     ; 

gj    rH     rH     rH     rH          ] 

III 

C30    rH    CO    GO    CO 

o|3 

O   O   O   O   O 

«j 

•S§3 

o  c  fc" 

'Si 

Q) 

CO    1C    Tf*    t» 

CM    O    O    CO       • 

Ijl 

gas  burned 

* 

p  ic  p  p 
co  cd  csi  "t 

t^    O    CO    1>- 

111 

•^    1C    O    C^l    <M 

vj;  l^     rH     (M     O5     O5 

^   rH     <M     <M     rH     rH 

O    O    C5    O    0 

o 

«4H            M                          n-i 

§ 

M 

O    1C    O    05        . 

S"!^  a   S 

1C    Ttl    CO    CO    Tt< 

| 

8 

CN    CO    CO    TH 
i—  1     CM     CO     rH 

|l|ir| 

^    GO     GO     i>»    I>-    ts>* 

"   0    0    0    0    0 

c 

I 

w 

^    05"    rH    CO       '. 

IP  1=1 

„    CNJ    00    (M    ^ 

1    rH    CO    rjn    0    o 
C>    O    0    0 

<M     CO     rH     CO 

o^     «     -g 

iS^hi 

CO    CO    Tf    TH    rH 
1   t^    rH    CO    !>•    t^ 

rH     rH     rH     rH 

Is  1 

O    O    C5   O   O 

1 

o 

1C    -*1    CM    <M 

1C    CO     rH     O 
CO    CO    CO    CO 

o  o  o  o     '. 

Ipf! 

.   rH    O5    rH    CO    CO 

oc  O^    *O    "^    O^    O5 

•^  o  o  o  o  o 

£ 

^           §> 

H 

«*-•  S          0! 

•r*    rH    CO    CO    1C    1C 
O    I"-    CO    1C    CM    rH 

ii-f^ii 

.    CO     CO    O    rH 
be  C^    CO    rH    CO 

•SP.2     £    o  ^ 

^     rH     rH     rH     rH 

i 

&i  s  °s 



!       :    .    . 

! 

i 

"     f-t 

rH 

6 

S-H 

. 

•                ••-?           •       $£) 

*3 

•>^         ti) 

>• 

'*        rH     -3            I     S 

x 

a 

N           *          pM 

"3           '     r-J                  CO 

.       JH      O              (M 

c 

i 

*o  *S3             + 

"S 

^        *     CO         r-       + 

>         .    °°    .S      02 

f 

50  1  +  *.  '§ 

o 

a 

®  'o  o   «  .g 

] 

! 

|2  ||i 

1 

|2|^1 

1 

i 

§>  i  1  +  § 

8 

c3"^  1  +  i 

•-S    tjo  S    a)  0~ 

^^       Vin    f^       O     /—C 

I  §  II  ~ 

«   fl  «§  jj  ^ 

B   P  -^  &VP 

r2       O     ^       O     "S 

P^  Q  PQ  <j  PH 

llltl 

PH  Q  pQ  ^  PH 

THE   GAS   TURBINE. 


179 


The  lean  gases  are  less  advantageous  in  this  respect  than 
the  richer  mixtures. 

We  may  therefore  reach  the  conclusion  that  the  nature 
of  the  combustible  (liquid  or  gaseous)  is  not  a  matter  of 
great  importance  from  the  point  of  view  of  the  total  probable 
efficiency  py,  but  that  the  lean  mixtures  are  less  advanta- 
geous than  rich  mixtures  because  of  the  unfavorable  influ- 
ence upon  the  mechanical  efficiency  when  the  work  of  com- 
pression acquires  great  importance. 

The  Gas  Turbine  from  a  Mechanical  Viewpoint. 
Flow  of  Gases  Through  Nozzles. 

According  to  the  principle  of  the  conservation  of  energy, 
the  velocity  of  discharge  w2  is  given  if  we  neglect  the  initial 
velocity  wl  of  the  gas,  by  the  relation: 


u\ 


if  the  evolution  undergone  by  the  gas  corresponds  to  an 
isothermal  compression,  followed  by  an  isobaric  combustion. 
For  the  group  of  cycles  exhausting  at  700  degrees,  we 
have: 


Compression  ratio. 

5 

10 

15 

20 

25 

30 

40 

60 

80 

100 

Q  —  g=  calories    .  . 

103 

162 

200 

236 

258 

283 

323 

388 

430 

471 

w2  =  metres  per  second 

927 

1162 

1288 

1400 

1466 

1533 

1637 

1794 

1892 

1975 

These  velocities  exceed  those  of  steam  in  ordinary 
steam  turbines  when  compression  ratios  of  15  to  20  are 
exceeded.  For  this  reason,  under  similar  structural  con- 
ditions for  the  revolving  disc,  the  efficiency  of  the  disc  itself 
will  be  less.  Fortunately  other  factors  act  in  the  opposite 
sense,  and  in  favor  of  the  gas  turbine. 

The  power  delivered  per  unit  of  terminal  section  of  a 
nozzle  is  greater  in  the  case  of  the  gas  turbine.  If  the  gas 


180 


THE   GAS   TURBINE. 


escapes  at  a  temperature  of  700  degrees  C.  absolute,  and 
at  atmospheric  pressure,  the  weight  of  a  cubic  metre  is 
about  0.5  kilogramme.  The  discharge,  by  weight,  will 
then  be  as  follows: 

for  w2  =  1000  m/s          1500  m/s          2000  m/s 

the  values  1.8  kg.  2.7  kg.  3.6  kg. 

per  square  millimetre  of  cross-section. 


Calories 

eooo, 


1000 


o 


FIG.  65. — Velocity  of  discharge  of 
steam  from  nozzles.  Cycle  with  isobaric 
combustion;  exhaust  at  700  degrees. 


0 


10 


FIG.  66. — Energy  in  calories  de- 
livered per  square  millimetre  of  termi- 
nal cross-section  of  nozzle. 


The  power  delivered  in  the  form  of  kinetic  energy  per 
square  millimetre  of  section  will  then  be  equivalent  to  the 
following  quantities  of  heat,  if  we  consider  the  same  group 
of  cycle  as  before: 


THE   GAS   TURBINE. 


181 


Pressure  of  combustion. 

5 

10 

20 

30 

40 

60 

80 

100 

Discharge  in  weight  kg    .      ... 

16 

2.1 

25 

2.75 

295 

320 

34 

36 

Power  delivered,  calories  

165 

340 

590 

780 

950 

1240 

1460 

1700 

If  the  exhaust  takes  place  under  a  pressure  reduced  to 
-  atmosphere  the  figures  for  the  power  delivered  will  be 

reduced  in  the  same  proportion. 

In  a  steam  turbine  operating  with  a  pressure  of  10 
atmospheres  and  against  a  pressure  of  yV  atmosphere  in  the 
condenser,  the  power  delivered  per  square  millimetre  of 
nozzle  is  equivalent  to  only  60  calories. 

The  Formula  of  Saint  Venant. 

If  a  gas  flows  through  a  passage  without  friction,  the 
initial  and  final  pressures  being  ajt  and  <o2,  and  the  velocities 
Wi  and  w2,  the  adiabatic  flow  is  represented  by  the  formula 
of  Saint  Venant: 


2        2  ^\ 

—Wi  I  r 

r     /   ^-F^' 

JiO2 


jf-w*      r 


(3) 

or  "  2g    —  rl1(^1-^).  (4) 

Velocity  of  a  Gas  Flowing  from  a  Reservoir  through  a  Nozzle. 

If  we  assume  the  velocity  of  approach  wl  as  negligible, 
we  have  at  any  point  of  the  nozzle  corresponding  to  a  pres- 
sure px,  a  velocity  wx  given  by  the  equation: 


wx  = 


and  since 


(5) 


182 


THE   GAS   TURBINE. 


we  have 


Vr 
^•J/s-y 
r—i  vJt\<t>i/ 


4fe<fc&t& 


FIG.  67. — Diagram  of  nozzle  velocities. 


(6) 


f | 

FIG.  68. — Diagram  of  nozzle  sections. 


We  readily  find  that  the  minimum  value  of  sx  (or  of  —  ) 

wx  ' 

corresponds  to  a  pressure  a>m,  given  by: 


(7) 


whence 


(8) 


/ 

IT  /o  r      /^mXY 

/7  =  Sm-t   /2^— f- rf--) 
V       *  f  +  lXttt/ 


and 


For  air  we  have  7- =  1.4  and  hence: 


(9) 


whence 


THE   GAS   TURBINE.  183 

It  can  be  demonstrated  that  pm  cannot  fall  below  this 
value,  and  that  wm  cannot  exceed  the  velocity  of  sound.* 

To  release  the  air  without  loss  of  energy,  down  to  the 
pressure  of  the  atmosphere;  or,  more  generally,  down  to  any 
given  pressure  p2,  we  must  therefore  use:  if  we  have  w2> 
0.529^,  a  converging  nozzle;  if  we  have  w2  <  0.529^,  a 
converging-diverging  nozzle.  The  latter  case  is  the  only 
one  to  be  considered  for  an  air  turbine,  in  which  we  always 
have  to2  =  l,  and  w1>1.9  kilogrammes. 

Length  and  Final  Section  of  Nozzle. 

In  practice  the  diverging  portion  of  the  nozzle  is  made 
in  the  form  of  a  cone  of  an  angle  of  about  10  degrees,  in 
order  to  avoid  the  breaking  of  the  vein,  which  cannot  follow 
the  walls  if  a  greater  angle  is  used.  The  final  section  s2, 
and  hence  the  length,  of  the  nozzle,  will  then  be  determined 
by 

(10) 


Vm 


1  ,~, (11) 


Since,  as  for  air,  we  have  a>m  =  0.529^,  we  have 


y-i 


52      ( r\  Kc>r\coi\y        /I — (0.529)   y  .  /ir>x 

-ji  =  (0.529-J      ^  / • '-^r-  (1^) 

Sm  (    «j  -y    -^ 


*  The  velocity  of  sound  in  a  gas  of  which  the  absolute  density  is  D  is 
given  by  the  formula  of  Newton: 


si 

E,  being  the  coefficient  of  elasticity  of  the  gas,  has  for  its  value  —  X  p.   We 
then  have  V— 


184 


THE   GAS   TURBINE. 


Thus,  for  example,  we  have,  for 


" 


Sm 


20; 


2.91. 


The  diagram  (Fig.  69)  shows  these  results.  It  will  be 
seen  that  the  ratio  of  cross-sections  for  a  given  expansion 
is  less  in  the  case  of  air  than  for  steam.  The  nozzle  will, 
therefore,  be  shorter. 


0         10        ZO        30        40 

Fio.  69. — Ratio  of  nozzle  sections  for  air  and  saturated  steam. 

This  relation  depends  wholly  on  —  and  not  on  the  tem- 
perature. 

Velocity  in  the  Neck  of  the  Nozzle. 

The  velocity  wm  in  the  neck  of  the  nozzle  depends  upon 
the  absolute  temperature  0lt  and  not  upon  the  relation  of 


THE   GAS  TURBINE.  185 

the  pressures,  as  is  shown  in  equation  (8),  in  which  we  may 
replace  aj^^  by  R6l 


r  -4-[  R6i  •  (13) 

Thus  we  have  for: 

7^  =  1000  1500  2000  2500 
tom=  484   593   685   765. 

metres  per  second. 

Velocity  of  Discharge. 

If,  in  equation  (5),  we  note  that: 


i/Ji 

0, 


we  have: 


Vf         —       1 
^-i4C;) Y  -'> 


which  demonstrates  the  correctness  of  our  original  result 
based  upon  the  principle  of  the  conservation  of  energy.* 

Influence  of  the  Lower  Pressure. 

We  have  already  seen  that  the  velocity  in  the  neck  of 
the  nozzle  is  entirely  independent  of  the  expansion  ratio, 
and  depends  wholly  upon  the  temperature  of  the  gas  before 
the  expansion.  Thus,  in  the  case  of  air,  the  pressure  in  the 
neck  of  the  nozzle  is 

0.529^. 

Beyond  the  neck  the  expansion  continues  and  the  velocity 
increases  regularly,  while  at  the  same  time  the  pressure  falls. 

*  Equations  (3)  to  (14)  have  been  taken  from  Stodola's  treatise  on  the 
steam  turbine;  also  figures  70  and  71. 


186  THE   GAS   TURBINE. 


If  the  cross-section  increases  as  the  square  of  the  distance 
from  the  neck  (a  conical  nozzle)  the  pressure  varies  accord- 
ing to  a  law  which  we  may  determine  by  taking  the  value 
of  the  velocity  at  each  point  (which  is  dependent  upon  the 
section),  calculating  the  resulting  variation  in  kinetic  energy 
(from  the  neck  to  the  point  under  consideration),  and  thence 
obtaining  the  temperature  and  the  pressure  for  the  given 
point,  according  to  the  law  of  adiabatic  expansion. 

If  the  angle  of  opening  is  given  it  will  then  be  possible 
to  determine  a  definite  pressure  for  the  terminal  section 
as  a  function  of  the  length  of  the  nozzle. 

The  question  arises :  What  will  be  the  result  if  the  medium 
into  which  the  gas  is  discharged  from  the  nozzle  has  a  differ- 
ent pressure  from  that  at  the  end  of  the  nozzle? 

The  experiments  of  Professor  Stodola  upon  steam  have 
shown  that  if  the  pressure  is  lower  than  that  of  the  exhaust 
it  will  produce  sound  waves,  the  pressure  varying  accord- 
ing to  a  sinusoidal  curve  in  the  discharge  chamber. 

Emden  has  calculated  for  air,  and  Prandtl  for  the  vapor 
of  water,  the  corresponding  wave  lengths. 

The  formula,  of  the  form: 

i—teL 


fV>m*        ,\/> 

"h--1) 


in  which  c  is  the  velocity  of  sound  in  the  discharge  chamber, 
and  wm  the  velocity  of  the  fluid  at  its  discharge,  shows  that 
the  waves  can  be  produced  only  when  the  velocity  of  dis- 
charge is  greater  than  that  of  sound  (Fig.  70).  Professor 
Stodola  admits  that  the  fluid  leaving  the  nozzle  expands  at 
once  to  the  pressure  of  the  surrounding  medium,  this  causing 
the  transformation  of  an  excess  of  the  potential  energy  of 
the  exhaust  fluid  into  living  force.  It  is  this  excess  which 
causes  the  sound  waves  and  which  is  transformed  into  heat 
by  friction  and  eddies. 

If  the  pressure  of  the  discharge  chamber  is  greater  than 
that  corresponding  to  the  terminal  section  of  the  discharge 


THE   GAS   TURBINE. 


187 


nozzle  a  sudden  shock  will  be  produced,  causing  a  rebound 
in  the  pressure  curve,  followed  by  strong  waves  (Fig.  71). 
This  rebound  may  even  force  its  way  back  into  the  nozzle, 
as  shown  in  curve  D. 

Absolute  Pressure 


vcw<wNS 


20        10         0         10         20       30        40        50        60% 
FIG.  70. — Pressure  waves  in  discharge  nozzles. 

If  the  counter  pressure  be  increased  until  it  reaches  the 
same  order  of  magnitude  as  the  original  pressure,  the  re- 
bound will  penetrate  further  and  further  back  into  the 
nozzle,  and  may  reach  as  far  as  the  neck.  This  condition 
will  be  attended  with  a  great  loss  of  energy. 

The  theory  of  shock  has  been  studied  by  Lord  Rayleigh, 
Weber,  Grashof,  Lorenz,  Prandtl  and  Proell,  Stodola,  and 
others.  These  researches,  of  much  theoretical  interest,  lead 
to  the  following  practical  conclusions: 

In  order  to  secure  adiabatic  expansion  from  plTl  to  p3T3, 
it  is  necessary  to  use  a  nozzle  of  well-defined  length. 
If  too  short  the  expansion  will  be  incomplete,  and  the  living 
force  produced  will  not  utilize  all  the  available  energy.  If  it 


188 


THE   GAS   TURBINE. 


is  too  long,  a  shock  will  be  produced,  accompanied  by  a  loss  of 
kinetic  energy.  The  best  length  of  nozzle  can  be  determined 
only  by  experiment.  In  practice  the  pressure  may  be  varied 
until  the  best  result  is  produced.  It  will,  therefore,  be  seen 
that  it  is  difficult  to  obtain  a  good  efficiency  with  an  explosion 
turbine,  in  which  pl  and  Tl  are  continually  varying,  and  in 
which  the  nozzle  will  be  alternately  either  too  short  or  too  long. 


1*6 


Absolute  Pressure 


FIG.  71. — Oscillations  in  discharge  nozzles. 

It  is  also  evident  that  any  method  of  regulating  a  turbine 
by  varying  the  maximum  pressure  must  be  accompanied  by 
a  loss  of  kinetic  energy.  It  is  possible  that  a  compensating 
action  may  be  obtained  by  varying  the  temperature  and  the 
maximum  pressure.  However  this  may  be,  the  best  method 
for  regulating  a  turbine  is  by  the  variation  of  the  admission. 

Influence  of  Friction. 

If,  according  to  Stodola,  we  designate  the  successive 
states  of  the  gas  in  two  distinct  sections  of  the  fluid  vein  by 
the  indices  1  and  2,  and  let  Q8  be  the  quantity  of  heat  dissi- 


_  THE   GAS   TURBINE.  _  189 

pated  by  radiation  and  conductivity  during  the  period  in 
which  the  gas  is  passing  from  one  of  these  sections  to  the 
other,  we  have: 


which  gives  the  formula  of  Zeuner: 


From  this,  taking  the  particular  case  of  adiabatic  flow, 
we  have: 


and  since  ^  =  constant  +CT 

w2    ™C 


If,  upon  an  infinitely  small  element  of  the  gaseous  mass  we 
consider  the  influence  of  the  walls  to  act  in  such  a  manner  as 
to  add  or  subtract  a  quantity  of  heat  dQ,  and,  on  the  other 
hand,  there  is  disengaged  by  friction  a  quantity  of  heat  dR, 
we  have: 


If  we  thus  introduce  the  idea  of  frictional  resistance,  we 
find  that  the  formula  of  Saint  Venant  thus  generalized  be- 
comes, in  the  case  of  adiabatic  flow  (E  =  0,  Q8  =  0)  • 


As  Professor  Stodola  has  remarked,  an  adiabatic  flow 
with  friction  is  not  adiabatic  in  the  same  sense  as  a  flow 
without  friction. 

The  work  of  friction  is  not  wholly  lost,  for  a  portion  is 
transformed  into  heat  and  acts  to  reheat  the  fluid,  thus  in- 
creasing the  amount  of  heat  transformed  into  work  in  the 
course  of  the  expansion. 


190 


THE   GAS   TURBINE. 


In  the  entropy  diagram,  the  successive  states  of  the  fluid 
during  the  flow  being  represented  by  the  curve  Ai}  A2,  the 
area  Al  A2  A"  A"  represents  the  total  work  of  friction, 
(R),  while  the  effective  loss  of  kinetic  energy  is  only  the  area 

A i  A2  A"  A" . 

T 


\ 


\Ai 


Bi  Ti  Ci 


0  A,"        Az  6 

Fio.  72.  —  Entropy  diagram  of  friction  losses  in  nozzles. 

Messrs.  Delaporte,  Lewicki,  and  Stodola  have  each  given 
the  figures  resulting  from  their  investigations  with  steam, 
showing  the  actual  losses  of  kinetic  energy  in  a  diverging 
nozzle  to  be  from  5  to  15  per  cent.* 

The  actual  loss  of  kinetic  energy  may  be  expressed  by 


in  a  cylindrical  tube.     For  a  conical  nozzle  it  is  necessary 
to  proceed  by  integration. 

*  Delaporte:  Nozzle  of  6  to  9  mm.  on  50  mm.,  discharging  into  the  atmos- 
phere, loss  5  per  cent. 

Lewicki:  Nozzle  of  6  to  7  mm.  on  30  mm.,  ratio  of  pressures  6.86,  loss  8 
per  cent. 

Stodola:  Nozzle  of  12  mm.  on  150  mm.,  losses  10  to  20  per  cent. 


THE   GAS   TURBINE.  191 

Classification  of  Gas  Turbines. — Efficiencies  of  Revolving  Discs. 
Losses  in  the  Blades. 

The  turbine  may  be  either  axial  or  radial,  and  composed 
of  one  or  several  discs. 

The  characteristic  feature,  however,  in  all  cases,  is  the 
difference  in  pressure  before  and  beyond  the  blades.  If 
this  difference  is  zero,  that  is  to  say,  if  the  pressure  in  the 
space  comprised  between  the  guide  blades  and  the  revolv- 
ing wheel  is  the  same  as  at  the  discharge  of  the  revolving 
buckets,  we  have  an  impulse  turbine.  In  turbines  of  this  class 
the  transformation  of  energy  takes  place  in  the  guide  nozzles, 
and  the  revolving  wheel  utilizes  the  force  thus  developed. 

If,  on  the  contrary,  a  difference  of  pressure  exists  we 
have  to  deal  with  a  reaction  turbine. 

The  reaction  turbine,  having  a  degree  of  reaction  of  1 : 2, 
operates  with  a  velocity  40  per  cent,  greater  than  that 
necessary  for  an  impulse  turbine.  For  the  same  tangential 
velocity  it  therefore  requires  double  the  number  of  revolving 
wheels. 

For  these  reasons,  and  especially  because  the  impulse 
turbine  lends  itself  to  the  use  of  a  single  expansion  and  does 
not  require  the  gases  to  be  discharged  upon  the  revolving 
wheel  until  after  they  have  been  cooled  by  their  expansion, 
the  reaction  type  has  not  been  applied  to  the  gas  turbine. 

The  impulse  turbine  with  several  wheels  may  be  con- 
structed either  with  velocity  stages  or  with  pressure  stages. 

The  advantages  of  using  multiple  discs  lies  in  the  fact 
that  the  same  hydraulic  efficiency  is  obtained  with  one- 
third  the  tangential  velocity  if  two  revolving  discs  are  used 
instead  of  one,  and  so  on. 

Unfortunately  it  is  not  yet  possible  to  determine  in  ad- 
vance the  efficiency  of  the  revolving  discs  of  future  gas  tur- 
bines. We  know  what  the  hydraulic  efficiency  should  be, 
neglecting  the  resistance  of  friction,  but  it  is  impossible. 


192  THE   GAS   TURBINE. 

without  previous  experiments,  to  determine  what  the  fric- 
tion of  the  hot  gases,  more  or  less  expanded,  will  be  upon  the 
fixed  and  moving  blades. 

It  seems  as  if  the  friction  should  be  less  than  in  the  case 
of  the  steam  turbine.  If  so,  the  number  of  revolving  discs 
might  be  increased,  thus  increasing  both  the  total  efficiency 
and  the  hydraulic  efficiency,  properly  so  called. 

In  steam  turbines  of  the  impulse  type  the  present  ten- 
dency is  to  multiply  the  number  of  pressure  stages  and  to  re- 
duce the  number  of  revolving  discs  in  each  stage.  It  would 
not  be  easy  to  carry  this  method  very  far  with  the  gas  tur- 
bine since  it  would  be  necessary  to  have  a  final  temperature 
of  less  than  700  degrees  absolute,  in  order  to  avoid  having 
too  high  temperatures  in  the  upper  pressure  stages.  This, 
as  we  have  already  seen,  would  necessarily  be  accompanied 
by  a  reduction  in  the  thermal  efficiency. 

There  are,  therefore,  in  the  case  of  the  gas  turbine,  cer- 
tain contradictory  influences,  of  which  the  final  effect  upon 
the  mechanical  efficiency  can  be  determined  only  by  experi- 
ment. Nevertheless,  everything  indicates  that  the  mechan- 
ical efficiency  of  the  gas  turbine  should  be  at  least  equal  to 
that  of  the  steam  turbine. 

Friction  of  Discs  Revolving  in  Air. 

In  existing  steam  turbines,  the  friction  of  the  revolving 
discs  is  the  cause  of  a  certain  loss  of  energy.  This  loss  is  less 
than  was  formerly  believed,  but  it  is  nevertheless  of  impor- 
tance. We  shall  see  that  this  friction  loss  will  be  rela- 
tively less  in  the  gas  turbine,  even  when  the  pressure  of  the 
fluid  is  equal  to  that  of  the  atmosphere.  At  the  present 
time  we  have  no  means  of  knowing  the  magnitude  of  this  re- 
sistance when  the  machine  is  operating  under  load.  The 
investigations  of  Odell,  Lewicki,  Stodola,  and  others,  have 
enabled  us  to  determine  the  amount  of  power  absorbed  by 
friction  when  operating  without  load. 


_  THE   GAS  TURBINE.  _  193 

It  should  be  noted  that  this  power  is  from  two  to  four 
times  greater  for  a  bladed  disc  revolving  in  the  atmosphere 
than  when  it  is  enclosed  in  a  chamber,  sealed  against  all 
ventilation.  Under  such  conditions,  a  bladed  disc  absorbs 
but  little  more  work  than  a  flat  disc.  The  work  of  friction 
is  proportional  to  the  cube  of  the  number  of  revolutions  and 
may  be  represented  by 


in  which  a  is  a  coefficient,  D  the  diameter  of  the  disc,  u 
the  tangential  velocity,  and  d  the  specific  gravity  of  the 
gas.  All  other  things  being  equal  there  is  absorbed  in 
saturated  steam  1.3  times  the  amount  of  work  that  is 
absorbed  in  air,  a  point  which  is  favorable  to  the  gas  turbine. 

Under  atmospheric  pressure,  steam  superheated  to  300 
degrees  Centigrade  offers  the  same  frictional  resistance  as  air 
at  the  ordinary  temperature. 

Lewicki  has  found  that  at  300  degrees,  and  under  a  very 
low  pressure,  the  amount  of  work  absorbed  is  a  little  less 
than  in  air  at  atmospheric  pressure. 

In  the  case  of  a  gas  turbine,  however,  with  an  exhaust  of 
600  degrees  absolute,  the  density  of  the  air  is  only 


and  we  conclude  that  the  loss  would  probably  be  less  than 
that  observed  in  the  steam  turbine. 

There  is  another  factor  which  should  reduce  still  further 
the  relative  importance  of  this  loss.  This  is  the  relatively 
small  size  of  the  discs  of  the  gas  turbine.  We  have  already 
seen  that  the  total  section  required  for  the  passage  of  the 
gas,  for  the  same  amount  of  work,  is  less  than  in  the  case  of 
the  condensing  steam  engine. 

In  consequence  it  may  be  possible,  at  least  in  the  case  of 
very  large  turbines,  to  reduce  the  diameter  of  the  revolving 
13 


194  THE    GAS   TURBINE. 

wheels.  For  small  units  the  diameter  is  controlled  by  the 
tangential  velocity  and  by  the  necessary  number  of  revolu- 
tions, and  this  may  not  be  reduced.  On  the  contrary,  the 
higher  velocity  of  the  flow  of  air  may  lead  to  larger  wheel 
diameters. 

Regulation  of  Gas  Turbines. 

The  question  of  speed  regulation,  a  matter  of  great  in- 
dustrial importance,  does  not  yet  appear  to  have  been  made 
the  object  of  any  important  effort.  Let  us  see  how  the  regula- 
tion of  a  turbine  with  a  single  nozzle  may  be  effected.  There 
are  two  cases  to  be  considered,  that  in  which  the  compressor 
is  not  mechanically  connected  to  the  turbine  wheel,  and  that 
in  which  a  direct  mechanical  or  electrical  connection  exists 
between  these  two  elements. 

In  the  first  case:     The  relation 


shows  that  the  power  delivered  by  a  nozzle  is  not  influenced 
very  strongly  by  a  variation  in  the  temperature  before  ex- 
pansion 6t  (which  is  the  temperature  of  combustion),  if 
the  ratio  of  pressures  is  not  varied. 

In  fact  the  kinetic  energy  of  a  unit  of  mass  is  propor- 
tional to  0t  but  the  density  of  the  gas  at  discharge  is  propor- 

tional to  a-;  the  pressure  oj2  not  varying.     The  velocity  w2 
ai 

being  proportional  to  V  Ql  the  power  developed,  propor- 
tional to  —^~,  is  proportional  to  -W  -1  X  Olf  or  to  yOv 


If  we  vary  the  ratio  of  pressures  —  without  modifying  Ol 
we  obtain  a  variation  of  62  proportional  to  (— 2J  7~.  From 
this  the  density  varies  as  ^-,  in  supposing  that  w2  is  fixed 


THE    GAS   TURBINE.  195 

and  that  w^  alone  varies.     The  flow  in  weight  is  then  pro- 
portional to 


,    .  mm?    . 

and  the  product  —^-  is  proportional  to 


If,  therefore,  we  act  solely  on  the  temperature  of  combus- 
tion, we  may  reduce  the  power  in  the  ratio  of  V  Ov  and  the 
temperature  of  the  exhaust  will  be  reduced  when  operat- 
ing at  light  loads.  The  efficiency  will  not  be  materially 
affected  (it  will  be  rigorously  unchanged  if  the  compression  is 
adiabatic). 

If  we  act  solely  on  the  pressure  of  combustion  the  tempera- 
ture of  the  exhaust  will  be  increased  as  the  power  is  reduced, 
a  condition  which  is  entirely  inadmissible,  since  it  would 
lead  to  higher  exhaust  temperatures  than  700  degrees  at 
light  loads.  If,  on  the  contrary,  we  arrange  that  the  ex- 
haust temperature  shall  not  exceed  700  degrees  at  light 
loads,  we  shall  have  a  lower  exhaust  temperature  under  full 
load,  and  the  efficiency  will  be  reduced. 

This  latter  inconvenience  may  be  avoided  and  a  more 
energetic  regulation  effected  by  causing  the  temperature  and 
the  pressure  to  vary  at  the  same  time,  in  such  a  manner  as  to 
keep  the  final  temperature  02  constant,  although  this  method 
will  lower  the  thermal  efficiency  at  light  loads. 

Under  these  conditions  the  density  does  not  vary;  the 
velocity  varies  as 


iu 


196  THE   GAS   TURBINE. 


and  the  energy  developed  varies  as 


If  the  reduction  in  pressure  is  produced  by  a  valve 
placed  between  the  combustion  chamber  and  the  compressor, 
the  efficiency  will  be  reduced  to  an  inadmissible  extent. 
In  such  a  case  it  will  be  advisable  to  use  an  independent 
compressor,  with  variable  compression. 

The  variations  in  flow  resulting  from  variations  of  6l  or 

of  — -  or  from  both  of  these  elements  at  the  same  time,  will 

cause  the  nozzles  to  operate  under  different  conditions  from 
those  for  which  they  were  designed,  when  the  machine  is 
under  light  loads.  This  will  reduce  their  hydraulic  efficiency ; 
on  the  contrary,  the  efficiency  of  the  revolving  discs  will  be 
increased.  Another  method  applicable  to  the  single  nozzle 
is  based  on  the  hit-or-miss  system.  So,  far  as  efficiency  is 
concerned,  this  is  probably  the  best  method,  since  the  vol- 
ume of  the  combustion  chamber  is  so  small  compared  to  the 
flow  of  gas  that  the  transition  periods  of  low  hydraulic 
efficiency  would  be  of  negligible  duration.  On  the  other 
hand,  some  method  of  re-ignition  would  be  required,  unless 
the  compression  and  temperature  were  sufficient  to  insure 
automatic  ignition. 

If  the  compressor  is  mechanically  or  electrically  connected 
to  the  turbine,  it  may  be  included  in  the  regulation  system 
by  causing  the  excess  production  to  be  accumulated  in  a 
reservoir  during  the  periods  when  the  demand  for  the  tur- 
bine is  below  normal. 

Let  us  now  consider  turbines  with  multiple  nozzles.  In 
such  cases  it  will  be  necessary  to  determine,  according 
to  the  conditions  of  each  particular  machine,  whether  it  is 
better  to  modify  the  discharge  of  a  single  nozzle  or  to  act 
proportionally  upon  them  all. 


THE   GAS   TURBINE.  197 

The  true  solution  appears  to  be  that  employed  in  the 
Curtis  steam  turbine,  by  shutting  off  a  certain  number  of 
nozzles  without  affecting  the  others.  This  method  should 
be  accompanied  by  the  use  of  a  fly-wheel  (or  accumulator 
of  energy)  if  great  regularity  of  speed  is  required,  or  if  there 
are  not  many  nozzles. 

It  will  be  necessary  to  control  the  gas  and  combustible  at 
each  nozzle  by  two  valves.  The  regulator  will  act,  through 
an  auxiliary  motor,  directly  upon  the  air  valves,  and  upon 
the  valves  controlling  the  combustible  by  means  of  a  small 
piston,  acting  only  when  the  pressure  in  the  combustion 
chamber  reaches  a  certain  value;  its  movement  being,  to  a 
certain  extent,  proportional  to  this  pressure. 

However  all  these  points  may  be,  it  is  evident  that  the 
question  of  the  regulation  of  the  gas  turbine  should  not 
present  any  serious  difficulties. 

Details  of  Qas=Turbine  Construction. 
Air  Compressors. 

We  have  seen  that  it  is  necessary  to  have  as  high  a  ratio 
of  pressures  as  possible  in  order  to  attain  a  high  efficiency, 
both  thermal  and  mechanical. 

It  appears  that  the  gases  which  are  delivered  into  the 
combustion  chamber  should,  therefore,  be  compressed  to 
about  40  atmospheres ;  or  else  that  a  lower  pressure,  say  about 
10  atmospheres,  be  used  in  connection  with  the  maintenance 
of  a  pressure  of  about  J  atmosphere  in  the  exhaust  space. 
In  the  second  case  it  is  evident  that  we  should  have  to  use  a 
second  compressor  to  raise  the  pressure  of  the  exhaust  gases 
from  J  atmosphere  up  to  atmospheric  pressure. 

In  order  that  the  work  required  for  this  operation  should 
not  exceed  that  required  to  produce  the  higher  initial  pres- 
sure of  40  atmospheres  it  is  necessary  that  the  absolute  tem- 
perature of  the  exhaust  gases  should  be  kept  down  to  a 
minimum  value  TQ  which  corresponds  to  the  temperature 


198  THE    GAS   TURBINE. 

of  the  atmosphere.  This  is  a  difficult  matter,  and  can  be 
effected  only  by  using  regenerators  or  tubular  coolers  of 
large  size;  or  by  using  injections  of  water,  involving  the 
employment  of  a  wet  air  pump,  or  possibly  a  barometric 
condenser  and  dry  air  pump. 

With  these  reservations  the  two  systems  may  be  con- 
sidered as  equivalent,  but  that  which  involves  the  employ- 
ment of  an  air  pump  is  principally  of  interest  so  far  as  it 
bears  upon  the  practicability  of  replacing  reciprocating  com- 
pressors with  turbine  air  compressors. 

In  practice  it  appears  to  be  difficult  to  attain  higher  de- 
grees of  compression  than  20  to  25  atmospheres  with  the 
turbine  compressor.  To  produce  such  pressures  it  is  neces- 
sary to  have  a  large  number  of  revolving  wheels,  rotating  at 
high  velocities;  and  as  these  must  be  in  a  fairly  dense  me- 
dium the  mechanical  losses  resulting  from  the  friction  of  the 
wheels  in  the  compressed  air  must  have  an  injurious  influ- 
ence upon  the  efficiency  of  the  machine. 

If  it  is  desired  to  avoid  the  use  of  piston  compressors 
it  appears  to  be  necessary  to  subdivide  the  operation  in  the 
manner  indicated  hereafter.  If,  on  the  contrary,  com- 
pressors of  the  reciprocating  type  are  permissible,  there  is 
no  difficulty  in  attaining  pressures  as  high  as  50  atmospheres. 
These  machines,  as  we  shall  see,  have  an  excellent  efficiency, 
which  is  a  most  important  feature  in  the  present  instance. 
At  the  same  time  they  add  greatly  to  the  bulk  of  the  appara- 
tus, and  take  from  the  gas  turbine  many  of  the  advantages 
possessed  by  the  steam  turbine. 

In  cases  in  which  the  bulk  of  a  large  compressor  is  a 
matter  of  importance  it  may  be  found  desirable  to  have  the 
reciprocatory  compressor  preceded  by  a  turbine  compressor, 
or  by  an  ordinary  rotary  compressor. 

For  example,  we  may  use  a  turbine  compressor  to  com- 
press the  air  to  a  pressure  of  4  atmospheres,  which  involves 
an  amount  of  work  equivalent  to  only  30  calories  per  kilo- 


THE   GAS   TURBINE.  199 

gramme,  and  then  complete  the  compression  by  the  use  of  a 
piston  compressor,  which  would  raise  the  pressure  from  4  to 
40  kilogrammes  per  square  centimetre  (4  to  40  atmospheres) 
with  an  expenditure  equal  to  46  calories. 

The  mechanical  efficiency  of  the  turbine  compressor  being 
assumed  to  be  equal  to  0.70  and  that  of  the  reciprocating 
compressor  to  0.85,  the  combination  would  have  an  effi- 
ciency of  0.59,  but  the  bulk  of  the  piston  compressor  would 
be  reduced  to  one-fourth  that  otherwise  necessary,  since  the 
volume  of  air  to  be  handled  is  reduced  to  one-fourth. 
We  then  have  as  available  the  following  three  plans : 
A  piston  compressor,  compressing  the  air  directly  to  40 
atmospheres;  a  turbine  compressor,  compressing  the  air  to 
4  atmospheres,  followed  by  a  piston  compressor  raising  it  to 
40  atmospheres;  or  a  turbine  compressor,  compressing 
the  air  to  10  atmospheres,  and  a  cooler  beyond  the  gas  tur- 
bine, followed  by  a  turbine  air  pump  taking  the  burned  gases 
at  J  atmosphere  and  discharging  them  into  the  atmosphere. 

Ordinary  Piston  Compressors. 

An  excellent  study  of  machines  of  this  type  was  given 
by  M.  Barbet  in  the  Genie  Civil  from  May  to  August,  1895. 
We  may  here  note  at  once  that  compressors  with  liquid 
pistons,  such  as  those  of  Sommellier,  Dubois,  and  Frangois, 
and  others,  are  too  bulky  to  be  considered  in  connection  with 
the  gas  turbine,  and  we  are,  therefore,  obliged  to  resort  to 
compressors  of  the  Colladon  type,  with  simple  injection  of 
water;  or  of  the  Mekarski  type,  using  several  stages  of 
compressors,  with  intercoolers. 

M.  Mekarski  has  constructed  a  number  of  vertical  com- 
pressors, operating  at  100  to  150  revolutions  and  compressing 
air  to  about  60  atmospheres,  taking  0.065  kilogramme  of 
air  per  revolution.  These  machines  have  four  single-acting 
cylinders,  arranged  in  tandem  pairs,  having  automatic 
valves,  and  provided  with  water  injection  in  the  low  pres- 


200  THE   GAS   TURBINE. 

sure  cjdinders,  the  high-pressure  cylinders  being  jacketed. 
The  volume  efficiency  was  about  67  per  cent.  The  effi- 
ciency in  work  may  be  computed  as  follows :  The  indicated 
power  of  the  engine  operating  the  compressor  was  97  horse- 
power, and  there  was  compressed  390  kilogrammes  of  air 
per  hour. 

Theoretically,  an  isothermal  compression  to  60  atmos- 
pheres would  require: 

42,308X390 


270,000 


61.1  h.p. 


The  efficiency  of  the  combined  air  compressor  and  steam 

AT  i 

engine,  was,  therefore,  -7^-=  0.63. 

y  / 

If  we  assume  the  efficiencies  of  the  compressor  and  the 
steam  engine  to  be  the  same,  their  value  would  be  1/0.63  = 
0.79.  This  shows  that  even  with  a  piston  compressor  of 
such  a  moderate  size  as  100  horse-power  a  mechanical 
efficiency  of  nearly  0.8  may  be  obtained.  Under  these  condi- 
tions one  horse-power  delivered  to  the  shaft  of  the  compressor 
would  furnish  5  kilogrammes  of  air  compressed  to  60  atmos- 
pheres. 

Taking  compressors  of  large  size  we  may  cite  the  vertical 
triple  expansion  machines  of  2000  horse-power,  built  by  the 
Creusot  Works  for  the  Paris  Compressed  Air  Company. 
The  air,  in  these  machines,  is  raised  to  7  atmospheres,  the 
ratio  thus  being  1 : 7.  The  air  cylinders  are  double  acting, 
and  are  arranged  tandem  with  the  steam  cylinders.  The 
compression  is  effected  in  two  stages,  with  a  pressure  of 
2.7  kilogrammes  per  square  centimetre  (38.4  pounds  per 
square  inch)  in  the  intermediate  reservoir.  The  air  cylin- 
ders have  no  water  jackets,  but  water  injection  is  used  in  the 
cylinders,  in  the  valve  chests,  and  in  the  intermediate  reser- 
voir. 

Operating  at  50  revolutions  per  minute,  these  machines 
handle  20,720  cubic  metres  of  air,  or  25,400  kilogrammes  per 
hour,  with  a  volumetric  efficiency  of  about  0.80. 


THE    GAS   TURBINE.  201 

According  to  tests  conducted  by  M.  Bourdon  and  by 
Professor  Gutermuth,  the  expenditure  of  one  horse-power 
indicated  on  the  pistons  of  the  steam  engine  compresses 
12.7  kilogrammes  of  air  to  the  ratio  of  1:7.  Other  tests  give 
a  combined  efficiency  for  the  engines  and  compressors  of 
about  0.90. 

In  these  machines  of  the  Paris  Compressed  Air  Company 
the  curve  of  compression  corresponds  closely  to  the  equation 

Jp^1'3  =  constant 

and  the  air  enters  at  a  temperature  of  -f  5°  C.  and  leaves  at 
+  25°,  while  an  adiabatic  compression  would  give  a  final 
temperature  of  +200°.  The  cooling  by  water  injection  thus 
appears  to  be  very  effective. 

As  a  final  example  of  a  compressor  operating  at  slow 
speed  we  may  cite  a  Strnad  machine,  of  which  tests  by 
Professor  Gutermuth  upon  one  of  300  horse-power  gave  the 
following  results : 

Ratio  of  compression 1  to  7.1 

Number  of  revolutions 50  to  70 

_,     .      theoretical  work  of  compression 

Ratio: .    ,.  —c : =  0.73 

indicated  power  of  engine 

~   t .      indicated  work  of  compression 

Ratio: r— r -5 : — - — —. =  0.84. 

indicated  work  of  engine 

It  follows  that  the  mechanical  efficiency  of  the  compres- 
sor, assuming  it  equal  to  that  of  the  engine  would  be  1/0.84 
=  0.92,  but  since  the  elevation  of  temperature  has  the  effect 
of  raising  the  value  of  the  ratio 

theoretical  work  of  compression 
indicated  work  of   compression 

to  a  value  0.87,  we  have  in  reality  an  efficiency  0.87x0.92 
=  0.80.  The  Strnad  compressor  is  a  two-stage  machine  with 
two  cylinders  in  tandem  with  the  steam  cylinders  of  a  com- 
pound engine.  It  is  characterized  by  an  injection  of  water 


202  THE    GAS   TURBINE. 

under  pressure  in  the  cylinders,  and  by  the  use  of  Corliss 
valves.  The  consumption  of  water  is  2.55  litres  per  cubic 
metre  of  air.  With  this  machine  one  horse-power  com- 
presses 12  kilogrammes  of  air  to  a  ratio  of  1:7. 

The  air  compressors  at  the  Billancourt  Works  of  the 
General  Omnibus  Company  of  Paris  have  an  indicated 
power  of  875  horse-power,  and  compress  3420  kilogrammes 
of  air  per  minute  to  a  pressure  of  80  kilogrammes  per  square 
centimetre  (1137.6  pounds  per  square  inch),  making  32 
revolutions  per  minute.  The  compression  is  effected  in 
three  stages:  4  kg.,  24.5  kg.,  and  80  kg. 

There  are  injected  two  kilogrammes  of  water  for  every 
kilogramme  of  air  in  the  low-pressure  cylinders.  With  the 
external  air  at  18°  C.  (64.4  F.)  the  temperature  of  the  com- 
pressed air  is  60°  C.  (140  F.). 

We  have: 


=  0.53  to  0.55 


^i  of  the  steam  engines 
Whence  the  efficiency  is  0.73  to  0.74. 

We  see,  therefore,  that  the  older,  slow-running  com- 
pressors which  we  have  examined  give  values  which  may 
be  taken  as : 

0.70  to  0.80  for  machines  of  100  to  1000  h.p. 
0.80  to  0.90  for  units  of  2000  h.p. 

Modern  High=Speed  Compressors. 

During  the  past  few  years  the  necessity  for  providing 
machines  adapted  for  direct  connection  to  electric  motors 
has  led  designers  to  produce  high-speed  air  compressors, 
capable  of  being  operated  at  speeds  of  500  to  600  revolu- 
tions per  minute  for  sizes  of  100  horse-power. 

At  the  Diisseldorf  exposition  there  was  shown  by  Messrs. 
Pokorny  and  Wittekind,  of  Frankfort,  a  compound  tandem 
compressor  with  Koster  valve  gear,  driven  by  an  electric 
motor  of  70  horse-power,  running  at  550  revolutions. 


THE   GAS   TURBINE.  203 

The  stroke  of  pistons  was  150  mm.  and  the  diameters  of 
cylinders  300  and  190  mm.  respectively.  This  machine 
compressed  about  750  kilogrammes  of  air  per  hour  to  a  pres- 
sure of  7  atmospheres.  Data  concerning  tests  upon  modern 
high  speed  compressors  will  be  found  in  the  papers  of 
Richter,  Lebrecht,  Biel,  etc.* 

Machines  of  this  type  offer  advantages  so  far  as  reduc- 
tion in  dimensions  are  concerned,  especially  if  preceded  by  a 
turbine  compressor.  If  the  latter  machine  is  used  to  com- 
press the  air  to  a  pressure  of  4  atmospheres  absolute,  the 
small  machine  described  above  would  be  available  to  com- 
press 3000  kilogrammes  of  air  from  4  to  28  atmospheres. 
This  would  be  sufficient  for  a  gas  turbine  of  600  horse- 
power. 

Rotary  Compressors. 

Rotary  compressors  have  not,  up  to  the  present  time, 
been  very  successful.  They  are,  however,  used  to  some  ex- 
tent for  moderate  and  small  powers. 

The  Compagnie  Generate  Electrique  of  Nancy  has  devel- 
oped the  Hult  rotary  steam  engine,  the  principle  of  which  is 
applicable  to  the  compression  of  air. 

Messrs.  Siemens  and  Halske  have  produced  a  rotary 
compressor,  adapted  only  to  small  sizes,  and,  being  without 
clearance  space  and  capable  of  direct  connection  to  electric 
motors,  may  be  used  for  compressions  of  a  ratio  1:3,  or  to 
produce  a  vacuum  as  low  as  1.5  mm.  of  mercury.  It  would 
be  interesting  to  know  the  efficiency  of  these  machines,  as 
they  might  be  applicable  for  use  with  an  initial  compression 
of  4  atmospheres  and  an  exhaust  pressure  of  TV  atmosphere, 
to  give  an  expansion  ratio  of  1 : 40.  These  machines  would 
be  adapted  only  to  small  gas  turbines. 

*  Richter:  Thermische  Untersuchung  an  Kompressoren,  Zeitschr.  d  Ver. 
deutscher  Ing.,  July,  1905.  Lebrecht:  Versuche  mit  raschlaufende  gas-com- 
pressoren,  Zeitschr.  d.  Ver.  deutscher  Ing.,  1905.  Biel:  Zeitschr.  d.  Ver.  deut- 
scher Ing.,  1905,  p.  540. 


204  THE   GAS   TURBINE. 

Turbine  Compressors. 

In  1902  M.  Rateau  directed  attention  to  the  properties 
of  high-speed  blowers,  showing  such  a  machine  connected 
directly  to  a  steam  turbine  making  10,000  to  20,000  revolu- 
tions per  minute.  This  blower,  with  an  efficiency  of  about 
0.60,  gave  a  compression  ratio  of  1  to  1.5.  By  coupling  a 
series  of  such  blowers  the  pressure  may  be  increased  in 
a  geometric  proportion,  giving  with  four  such  blowers  a 
pressure  of  (1.5)4,  or  about  5  atmospheres  absolute. 

Theoretically,  the  efficiency  of  such  an  arrangement  is 
equal  to  the  efficiency  of  a  single  wheel.  Nevertheless, 
it  does  not  appear  to  be  practicable  to  use  this  machine 
for  pressures  much  higher  than  5  atmospheres,  since  the 
frictional  resistance  in  atmospheres  of  higher  densities  will 
increase  to  an  extent  which  causes  the  efficiency  to  fall  off 
materially. 

If  a  machine  of  this  type  is  used  to  lower  the  exhaust 
pressure  of  a  turbine,  the  above  inconvenience  does  not 
appear,  and  a  greater  number  of  wheels  will  not  be  required 
to  produce  the  desired  reduction  in  pressure.  At  the  same 
time  the  apparatus  will  have  to  be  much  larger  for  the  same 
discharge  of  gases  by  weight. 

For  example,  if  it  is  desired  to  produce  a  pressure  of  i 
atmosphere,  the  first  wheel  will  produce  a  reduction  of  only 
-¥-  =  0.1  atmosphere. 

It  follows  that  n  wheels  will  give  a  final  pressure  equal 
to  0.2  X  (1.5)n,  and  we  should  have  0.2  X  (1.5)n  =  l,  whence 
(1.5)n  =  5,  and  n  =  4.  It  is  understood  that  this  assumes 
that  the  exhaust  gases  have  been  cooled  to  the  temperature 
of  the  air  before  entering  the  apparatus. 

If  this  arrangement  is  employed  it  is  very  desirable  that 
the  multicellular  blower  should  be  connected  directly  to  the 
gas  turbine;  but  since  the  tangential  velocity  of  the  blower 
should  reach  260  metres  per  second  to  obtain  the  pressure 


THE   GAS  TURBINE.  205 

ratios  given  above,  a  high  rotative  speed  becomes  necessary 
(20,000  revolutions  in  a  machine  of  200  horse-power  com- 
pressing air  from  1  to  5  atmospheres). 

If  the  gas  turbine  is  designed  for  driving  dynamos, 
etc.,  it  should  make  not  more  than  1000  to  2000  revolutions. 
In  such  cases  it  would  probably  be  advisable  to  have  a  sep- 
arate turbine  to  drive  the  blowers. 

Besides  the  investigations  of  M.  Rateau  several  other 
attempts  have  been  made  to  utilize  the  turbine  compressor. 

In  England  experiments  have  been  made  with  the 
Parsons  turbine,  while  similar  attempts  have  been  made  by 
the  General  Electric  Company  to  utilize  the  Curtis  turbine. 
No  practical  results,  however,  have  yet  been  made  public. 

The  idea  of  Burdin  and  Tournaire  has,  therefore,  not  yet 
entered  into  practical  operation,  but  it  appears  to  be  on  the 
eve  of  successful  application. 

Thermal  Regenerators. 

The  application  of  alternating  regenerators,  necessary 
for  use  with  piston  engines,  does  not  appear  to  have  given 
practical  results.  The  question  appears  in  a  different 
light,  however,  when  considered  in  connection  with  the  gas 
turbine. 

In  the  latter  case  the  gases  issue  from  the  turbine  in  a 
continuous  manner,  with  a  fairly  high  velocity,  which  is  a 
great  advantage  in  connection  with  the  transmission  of  heat. 

The  gases  to  be  heated  are  also  delivered  in  a  continuous 
manner  by  the  compressor,  and  in  view  of  the  high  pres- 
sures under  consideration  the  losses  involved  in  producing 
a  rapid  circulation  in  a  system  of  tubes  need  not  be  very 
serious. 

The  burned  gases  discharged  by  a  gas  turbine  would  be 
much  cleaner  than  those  dealt  with  in  the  case  of  super- 
heaters attached  to  steam  boilers,  or  than  those  discharged 
from  reciprocating  gas  engines;  the  continuous  combustion 


206  THE   GAS   TURBINE. 

under  pressure  being  that  which  leaves  a  minimum  amount 
of  residue.  We  have  also  seen  that  these  gases  have  a  very 
slight  oxidizing  action.  These  conditions  are  all  favorable 
to  the  use  of  the  regenerator. 

Regeneration  from  Gas  to  Gas. 

Devices  intended  to  heat  the  compressed  air  by  means  of 
the  heat  abstracted  from  the  exhaust  gases,  are  analogous  to 
steam  superheaters  and  are  operated  under  similar  temper- 
ature conditions.  They  are  less  subject  to  oxidation,  the 
gases  being  poor  in  oxygen,  and  the  temperatures  are  more 
uniform. 

The  nature  of  the  metal  used  is  immaterial,  so  far  as  the 
transmission  of  heat  from  gas  to  gas  is  concerned.  Tubes 
either  of  iron  or  steel  may  be  employed.  Copper  or  alumi- 
num tubes  are  of  interest  only  as  regards  increased  durabil- 
ity. High  circulation  velocities  are  essential,  and  the  coun- 
ter-current principle  should  be  adopted,  taking  the  necessary 
structural  precautions  against  injury  from  expansion  and 
contraction. 

Regeneration  by  Steam. 

When  the  regeneration  of  the  waste  heat  is  effected 
by  the  aid  of  steam,  the  latter  is  generated  in  a  boiler  of  the 
instantaneous  flash  type,  heated  by  the  exhaust  gases. 
Such  a  boiler  includes  a  reheater,  followed  by  the  boiler 
proper,  and  by  a  superheater,  all  with  a  systematic  circula- 
tion. These  three  portions,  however,  are  not  necessarily 
clearly  defined.  We  may  use,  for  example,  a  boiler  of  the 
Serpollet  type,  or  one  of  the  system  proposed  by  Col.  Renard.* 

The  water,  entering  at  one  end,  travels  continuously 
through  until  it  reaches  the  other  extremity  in  the  state 
of  superheated  steam.  Here,  as  before,  the  gases  should 
circulate  very  rapidly. 

*  See  Ge"nie  Civil,  1905. 


THE    GAS   TURBINE.  207 

Production  of  the  Combustible  Mixture. 

The  combustible  employed  may  be  solid,  liquid,  or 
gaseous,  but  it  is  improbable  that  a  turbine  employing  a 
solid  combustible  will  soon  be  realized.  It  would  un- 
doubtedly be  very  difficult  to  inject  a  solid  combustible  into 
a  combustion  chamber  against  a  pressure  of  30  to  40  atmos- 
pheres, and  the  ashes  discharged  with  the  burned  gases 
would  cause  excessive  wear  upon  the  blades  of  the  turbine. 

The  gas  turbine  is,  therefore,  not  adapted  for  the  direct 
use  of  solid  combustibles,  and,  for  a  long  time,  at  least, 
the  use  of  a  gas  producer  must  be  considered  necessary. 

Gaseous  Fuel. 

As  we  have  already  seen,  the  lean  gases  are  almost  as 
advantageous  as  the  richer  gases.  In  the  case  of  Dowson 
gas  the  air  compressor  must  deliver  a  volume  of  air  equal 
to  1.2  times  that  of  the  gas.  This  involves  the  use  of  two 
compressors  of  different  power  and  capacity. 

It  may  be  suggested  that  the  Gardie  system  is  available 
for  this  purpose,  in  view  of  the  fact  that  it  utilizes  the  sen- 
sible heat  of  the  gases  which  leaves  the  producer  at  about 
700  degrees  and  which  is  ordinarily  lost;  but  the  operation  of 
a  gas  producer  under  a  pressure  of  more  than  10  atmospheres 
appears  to  be  a  difficult  problem.  It  would  thus  be  neces- 
sary to  operate  the  producer  under  a  moderate  pressure,  a 
method  practicable  only  when  the  turbine  is  operated  with  a 
low-pressure  exhaust.  The  principal  advantage  of  this  sys- 
tem appears  to  lie  in  the  avoidance  of  any  wasting  of  the  gas. 

If  we  use  the  waste  gases  from  blast  furnaces  it  will  also 
be  necessary  to  have  two  compressors  of  different  dimen- 
sions, the  volumes  being  in  the  proportion  of  0.7  to  0.9  of  air 
to  1  of  gas. 

It  would  be  difficult  to  use  a  regenerator  in  this  case,  for 
it  is  well  known  that  the  large  amount  of  dust  contained  in 


208  THE   GAS   TURBINE. 

furnace  gases  renders  their  use  difficult  under  steam  boilers. 
This  difficulty,  however,  is  not  impossible  of  removal,  and 
the  use  of  the  regenerator  would  enable  improved  efficiency 
to  be  secured. 

With  very  rich  gases,  such  as  illuminating  gas  or  acety- 
lene, a  very  small  compressor  would  be  required  for  the  gas. 
The  relations  of  the  volumes  to  be  compressed  would  be, 
respectively,  as  1  to  8  and  as  1  to  20.  The  total  value  of 
the  work  of  compression,  however,  is  not  much  less  than  in 
the  case  of  lean  gases. 

With  liquid  combustibles  a  very  small  pump,  consuming 
but  little  power,  is  required,  but  the  air  compressor  demands 
about  as  much  power  as  the  two  pumps  together  in  the  case 
'of  gaseous  fuel. 

Liquid  combustibles  are  used,  either  by  volatilization 
in  a  carburetor,  similar  to  those  employed  for  gasoline 
motors,  or  by  direct  injection  into  the  combustion  chamber 
in  connection  with  some  sort  of  pulverizer  or  atomizer.  It 
may  also  be  found  advantageous  to  heat  or  volatilize  the 
liquid  fuel  by  means  of  the  heat  of  the  exhaust  gases. 

In  turbines  using  an  injection  of  water  or  steam,  the 
injection  may  be  made  either  in  the  combustion  chamber  or 
before  entering  it.  We  are  inclined  to  favor  the  latter 
solution,  especially  in  the  case  of  steam. 

The  Combustion  Chamber. 

The  dimensions  of  the  combustion  chamber  should  be 
such  that  the  reaction  may  be  completed  before  the  gases 
leaving  the  zone  of  combustion  penetrate  the  nozzle. 

According  as  the  maximum  temperature  Tl  varies  from 
1000  degrees  to  2500  degrees  absolute,  the  velocity  in  the 
throat  of  the  nozzle  varies  from  500  to  800  metres  per 
second.  If  we  take  a  temperature  of  2000°  C.  absolute, 
we  have  a  velocity  of  685  metres  per  second.  For  the 
terminal  part  of  the  section  of  the  nozzle  we  have,  for  a 


THE   GAS   TURBINE.  209 

compression  ratio  of  25  to  30,  and  a  temperature  of  700°  at 
the  end  of  the  expansion,  a  velocity  of  1500  metres  per 
second.  What,  then,  should  be  the  length  of  the  combus- 
tion chamber,  under  these  conditions?  Taking  a  tempera- 
ture of  2000°  absolute,  and  a  pressure  of  25  atmospheres,  the 

density  will  be:  (25  to  30)  X  2000  =  8'75  to  10'5  times  that 
of  the  exhaust  gases;  let  us  say  10  times.  If,  then,  the 
section  of  the  combustion  chamber  is  equal  to  that  of  the 
lower  terminal  section  of  the  nozzle  we  should  have  a 
velocity  one-tenth  as  great,  or  about  150  metres  per 
second. 

It  is  generally  admitted  that  the  velocity  of  propagation 
of  flame,  at  atmospheric  pressure,  is  only  about  1  to  2  metres 
per  second.  It  would  therefore  be  necessary  to  give  the 
combustion  chamber  a  section  of  about  100  times  that  of  the 
end  of  the  nozzle,  in  order  that  the  combustion  may  be 
absolutely  complete.  The  best  dimensions  can  be  deter- 
mined only  by  experience.  It  is  hardly  probable  that  such 
a  size  as  indicated  above  would  be  necessary,  for  with  the 
temperatures  and  pressures  under  consideration  the  com- 
bustible would  ignite  spontaneously,  and  hence  the  velocity 
of  propagation  of  the  flame  would  become  almost  infinite. 

In  practice  it  seems  as  if  a  cross-section  10  times  as  great 
as  that  of  the  terminal  section  of  the  nozzle  ought  to  be 
sufficient.  This  .would  give  a  velocity  in  the  chamber  of 
about  iV  that  of  the  discharge,  or  about  38  metres  per  second 
This  velocity  would  be  considered  normal  in  ordinary  gas 
mains,  operating  under  atmospheric  pressure. 

The  length  of  the  combustion  chamber  may  be  fixed 
at  5  to  10  times  its  diameter,  but  there  is  no  special  rule 
governing  this  dimension. 

For  example,  suppose  we  take  a  nozzle  having  a  terminal 
section  equivalent  to  that  of  a  circle  10  mm.  in  diameter, 
and  make  the  diameter  of  the  combustion  chamber  50  mm., 

14 


210  THE   GAS   TURBINE. 


we  get  a  velocity  in  the  latter  of: 

38  m.  per  sec. 

•% —    -  =15.2  m.  per  sec. 
Z.o 

If  we  give  the  chamber  a  length  of  300  mm.,  the  gas  will 
be  in  it  for  about: 

0.30  m. 

—  =  0.02  second. 


15.2  m.  per  sec. 

This  corresponds  to  the  duration  of  the  combustion  in  a 
gasoline  motor  making  1500  revolutions  per  minute. 

Nozzles  for  Injection  and  Expansion. 

In  the  case  under  consideration  there  are  many  reasons  in 
favor  of  partial  injection. 

The  injection  nozzles,  or  ring  of  fixed  blades,  being  sub- 
jected to  the  high  temperature  of  combustion,  it  is  necessary 
in  their  construction  to  provide  a  material  possessing  special 
properties,  including  resistance  to  heat  and  to  chemical  reac- 
tions, also  to  repeated  expansion  and  contraction,  and  finally 
possessing  considerable  mechanical  strength. 

These  conditions  are  well  filled  by  the  material  carborun- 
dum, with  the  exception  of  the  fact  that  precautions 
must  be  taken  with  respect  to  its  rather  high  conductivity 
for  heat. 

The  Combustion  Chamber  and  the  Nozzles  for  the  Characteristic 
Portion  of  the  Gas  Turbine. 

The  simplest  arrangement,  applicable  to  small  turbines, 
consists  of  the  combination  of  a  combustion  chamber  and 
single  diverging  nozzle,  the  latter  preferably  of  rectangular 
cross-section.  The  terminal  portion  of  the  nozzle  may  be 
made  of  metal,  since  the  gases  at  this  point  will  be  cooled 
to  below  800°.  The  end  of  the  nozzle  may  be  divided  by 
thin  partitions,  thus  forming  a  portion  of  the  distributing 
ring. 


THE   GAS   TURBINE. 


211 


Construction  of  the  Revolving  Wheels. 

The  construction  of  the  revolving  wheels  of  the  gas 
turbine  does  not  differ  materially  from  that  already  fol- 
lowed for  the  steam  turbine.  The  arrangement  of  a  single 
disc  may  be  adopted  or  that  of  multiple  discs;  the  latter  is 
preferable,  since  the  velocity  of  the  fluid  will  be  at  least  as 
high  as  in  the  steam  turbine. 

The  practical  design  depends  upon  the  linear  speed, 
and  the  moderate  velocity  of  120  to  200  metres  per  second  at 
the  perimeter  of  the  wheels  may  be  maintained. 

It  must  be  considered  that  the  temperature  of  300°  to 
400°  Centigrade  is  somewhat  higher  than  ordinarily  exists 
in  the  steam  turbine,  and  it  is  desirable  to  select  materials  of 
which  the  strength  is  reduced  as  little  as  possible  at  these 
temperatures.  No  serious  difficulties  need  be  apprehended 
on  this  score.  Steam  turbines  of  the  Laval  type  have  been 
operated  with  steam  superheated  to  600°  absolute  and  with 
air  heated  to  700°  absolute,  without  any  difficulty.* 

Tests  upon  nickel  steel  have  given  the  following  results: 


Absolute  temperature. 

300 

500 

600 

700 

Breaking  load  (kg.  per  cm.2)  

81 

91 

92 

73 

Elastic  limit  (kg  per  cm  2)  .  .  .  . 

70 

60 

54 

40 

Elongation  per  cent 

107 

87 

83 

70 

Reduction  of  section,  per  cent 

608 

60 

608 

70 

We  may  expect  that  the  light  metal  blades,  when  sub- 
jected to  the  oxidizing  action  of  the  gases  at  these  tempera- 
tures will  wear  somewhat  more  rapidly  than  the  blades  of 
the  steam  turbine.  In  the  latter  machine,  however,  it  is 
admitted  that  the  principal  cause  of  wear  is  due  to  the  action 
of  particles  of  moisture.  In  the  case  of  superheated  steam, 
and  consequently  with  the  gases  of  the  gas  turbine,  the  wear 

*  See  Lewicki:  Zeitschr.  d.  Ver.  deutscher  Ing.,  1905. 


212 


THE   GAS   TURBINE. 


of  the  blades  is  negligible.  The  burned  gases  contain  but  a 
small  proportion  of  free  oxygen  (5  to  10  per  cent.),  and 
nickel  steel  is  especially  resistant  to  oxidizing  influence. 

(C)  Cycle  with  regeneration 
of  heat   71-0.75 


(A)Cyc!e  without  regeneration 
of  heat 


FIG.  73. — Diagrams  showing  the  distribution  of  heat  from  the  combustion  of  1  kilo- 
gramme of  gas.  Water-injection  not  included..  Isothermal  compression;  isobaric  combus- 
tion at  a  pressure  of  40  atmospheres. 

General  Design  of  a  Gas  Turbine. 

Let  us  How  apply  the  preceding  theoretical  calculations 
to  three  practical  examples. 

For  this  purpose  we  will  select  a  system  employing  iso- 
thermal compression,  with  combustion  under  constant  pres- 
sure; the  turbine  being  intended  to  develop  150  horse-power, 
and  thus  capable  of  driving  a  dynamo  of  100  kilowatts. 


THE   GAS   TURBINE. 


213 


§    Ulip    p      ^S£  P  P 


CO 

cn  en 


p. 
3         B         r 


214  THE   GAS   TURBINE. 

The  pressure  ratio  will  be  taken  at  40,  and  this  may  be 
attained  either  with  the  exhaust  at  atmospheric  pressure  or 
with  exhaust  at  |  atmosphere;  in  this  latter  case  the  pressure 
of  combustion  will  be  9  atmospheres  above  perfect  vacuum. 

We  will  consider  the  following  cases : 

A.  Illuminating  oil  with  a  lower  calorific  value  of  10,000 

calories,  without  regeneration. 

B.  Same  data,  with  steam  regeneration,  with  /*=0.75. 

C.  Same  data,  with  regeneration  of  gas  to  gas,  /*=0.75. 
The  results  of  the  computations  are  given  in  the  preceding 

table.  The  figures  must  be  understood  as  having  only  a 
relative  value,  owing  to  the  numerous  hypotheses  which 
have  been  made  in  deriving  them.  Their  comparative 
value,  however,  remains  unaffected.  We  see,  for  example, 
that  the  injection  of  steam  permits  the  reduction  in  capacity 
and  power  of  the  compressor  by  about  one-third,  but  that 
this  increases  the  velocity  of  discharge  about  15  per  cent, 
to  the  detriment  of  the  mechanical  efficiency  of  the  machine. 
The  diagrams  on  page  212  will  be  of  interest,  as  showing 
the  distribution  of  heat  and  work. 

Experimental  Researches  Necessary  to  Determine  Precise  Data 
for  Gas  Turbine  Calculations. 

We  are  now  led  to  consider  what  experimental  data  are 
to  be  determined  in  order  that  we  may  substitute  more  or 
less  precise  computations  for  the  hypothetical  ones  which 
have  thus  far  been  employed  in  our  investigations. 

Above  all  things  it  is  desirable  that  a  study  should  be 
made  of  the  work  absorbed  in  the  compression  and  of  the 
final  temperature  of  the  compressed  gases.  There  appears  to 
be  no  experimental  difficulty  in  making  these  determina- 
tions. It  is  especially  desirable  that  these  studies  should  be 
made  with  rotary  compressors,  since  the  subject  of  piston 
compressors  has  already  been  well  investigated. 


THE   GAS  TURBINE.  215 

Further,  it  is  desirable  that  the  phenomena  of  combustion 
should  be  studied,  especially  to  determine: 

1.  The  limits  to   the  amount  of   combustible  and   air 
which  can  be  used  when  attaining  a  perfect  combustion  at 
different  pressures. 

2.  The  real  temperatures  of  combustion  thus  attained. 

3.  The  conditions  of  temperature  and   pressure  which 
will  insure  the  self-ignition  of  the  mixture. 

4.  The  time  required  to  enable  a  perfect  combustion  to 
be  realized,  and  thus  the  volume  of  the  combustion  chamber 
to  be  determined. 

5.  The  influence  of  these  various  elements  upon  the  veloc- 
ity of  the  gaseous  current. 

6.  The  influence  of  a  greater  or  less  quantity  of  vapor 
of  water  in  the  mixture.     This  should  include  the  extent  to 
which  any  portion  of  the  water  is  dissociated,  and  under 
what  conditions. 

It  is  not  difficult  to  see  what  methods  might  be  employed 
to  carry  out  such  a  programme.  The  present  electrical 
appliances  for  determining  high  temperatures  are  already 
available  for  such  a  purpose. 

It  would  then  be  desirable  to  investigate  the  subject  of 
expansion.  It  is  important  to  determine  the  extent  to 
which  the  temperature  is  lowered  by  expansion.  This  is  the 
most  delicate  part  of  all  the  investigations. 

While  it  is  comparatively  easy  to  measure  the  tem- 
perature before  expansion  and  the  pressures  before  and 
beyond  the  nozzle,  it  is  much  more  difficult  to  determine 
the  true  temperature  of  a  gas  leaving  a  nozzle  at  a  high 
velocity. 

The  thermometric  element  placed  in  the  midst  of  the 
gaseous  current  which  is  flowing  at  a  velocity  of  1200  to  1800 
metres  per  second,  takes  a  temperature  higher  than  that  of 
the  gas,  for  the  heat  disengaged  by  friction  is  not  dissipated 
by  radiation.  In  every  case  it  is  necessary  that  the  thermo- 
metric element  should  have  a  higher  temperature  than  that 


216  THE   GAS   TURBINE. 

of  the  surrounding  medium  in  order  that  the  heat  thus  dis- 
engaged may  be  removed  and  a  stable  condition  secured. 

Since  we  are  ignorant  of  the  value  of  the  velocity  (this 
involving  a  knowledge  of  the  temperature  of  the  gas),  it  is 
hardly  practicable  to  be  able  to  make  a  correction.  It  is, 
therefore,  necessary  to  compute  the  temperature  or  the  veloc- 
ity by  a  series  of  successive  approximations. 

It  seems  preferable  to  leave  aside  any  attempts  to  meas- 
ure the  final  temperature  of  expansion,  and  to  determine 
rather  the  kinetic  energy  of  the  gases  leaving  the  nozzle. 
This  may  be  done  by  measuring  directly  the  push  of  the 
gaseous  current  upon  a  turbine  blade,  as  has  been  done  by 
Delaporte,  Rateau,  Stodola,  and  others. 

Having  thus  determined  the  velocity  of  discharge  w21 
we  may  deduce  the  temperature  of  the  discharging  gases 

from  the  formula: 

?/> 2 


We  can  then  deduce  a  value  of  ?  which  takes  into  account 
the  friction  in  the  jet.  Experiments  of  this  kind  will  enable 
the  best  form  of  nozzle  to  be  determined,  as  has  already  been 
done  with  the  steam  turbine,  and  especially  to  permit 
the  question  whether  the  form  of  constant  acceleration  pro- 
posed by  Proell  is  preferable  to  the  ordinary  conical  form. 

Finally  it  is  desirable  to  make  an  experimental  determi- 
nation of  the  value  of  the  coefficient  of  transmission  of  heat 
from  one  gas  to  another  through  the  walls  of  an  assemblage 
of  tubes,  in  order  to  aid  in  determining  the  dimensions  of 
heat  regenerators. 

The  Future  of  the  Gas  Turbine. 

Having  now  discussed  the  question  of  the  construction 
of  the  gas  turbine  we  may  take  up  the  subject  of  the  future 
in  store  for  machines  of  this  kind. 

Their  great  theoretical  interest  has  been  apparent  to  all 
those  who  have  examined  these  questions  since  the  period 


THE   GAS   TURBINE.  217 

when  the  success  of  the  turbine  of  Laval  demonstrated  the 
value  of  the  pressure  type  of  steam  turbine.  This  cele- 
brated inventor  follows  the  thought  of  Burdin  and  Tournaire, 
and  suggested  very  early  the  idea  of  constructing  a  gas  tur- 
bine. Many  years  have  now  passed,  however,  without  the 
practical  realization  of  this  idea. 

Other  investigators  have  taken  up  the  same  idea, 
but  thus  far  their  efforts'  have  not  reached  commercial  suc- 
cess, while  during  the  same  period  the  steam  turbine  has 
emerged  from  the  experimental  workshop  and  acquired  its 
well-known  position  among  heat  engines. 

This  should  offer  no  reason  for  surprise,  when  we  con- 
sider the  multiplicity  of  technical  difficulties  which  present 
themselves  in  the  realization  of  a  practical  gas  turbine. 
The  success  of  the  steam  turbine,  however,  has  elicited 
investigations  of  the  greatest  interest  which  lead  us  to 
approach  the  construction  of  a  gas  turbine  without  hesita- 
tion. Some  investigations  are  yet  required  to  enable  the 
determination  of  the  conditions  of  combustion  and  the  exact 
laws  governing  the  expansion.  When  these  have  been  com- 
pleted we  will  be  in  possession  of  all  the  data  necessary  for 
the  turbine  itself  without  guesswork. 

Rotary  compressors,  multicellular  blowers,  turbine  com- 
pressors of  the  Parsons,  Curtis,  and  other  types,  are  rela- 
tively further  from  a  definite,  practical  solution,  but  every- 
thing leads  us  to  believe  that  no  material  delay  will  occur  in 
this  direction. 

We  may  thus  expect  to  see  commercially  produced,  a 
gas  turbine,  uniting  in  a  certain  degree  the  advantages  of  the 
gas  engine  and  the  steam  turbine. 

Without  overlooking  the  inconvenience  resulting  from 
the  presence  of  a  compressor  distinct  from  the  motor  itself, 
the  gravity  of  this  objection  may  be  exaggerated. 

If  we  are  willing  to  accept  the  piston  compressor  (or  use 
the  alternative  of  the  reduction  of  exhaust  pressure  below 
atmosphere)  the  gas  turbine  presents  the  same  advantages 


218  THE   GAS   TURBINE. 

of  moderate  bulk  and  weight  which  have  made  the  success  of 
the  steam  turbine. 

The  thermal  efficiency  of  the  new  machine  will  be  supe- 
rior to  that  of  the  gas  engine,  but  the  lower  mechanical 
efficiency  of  the  gas  turbine  will  reduce  the  total  useful 
effect  to  about  the  same  order  as  that  of  the  Diesel  motor; 
while  motors  using  blast  furnace  gases  should  give  an  effec- 
tive horse-power  with  an  expenditure  of  2000  calories. 

It  does  not  appear  that  any  sensational  invention 
can  modify  these  results  materially  in  the  future.  It  is  only 
by  continual  improvements  in  structural  details  that  the 
mechanical  efficiency  may  be  increased  by  the  reduction  of 
mechanical  losses. 

The  gas  turbine  will  not  be  a  universal  panacea,  neither 
will  it  dethrone  the  steam  turbine.  When  we  have  to  deal 
with  the  combustion  of  ordinary  coal,  nothing  can  surpass 
the  steam  boiler. 

But  for  other  combustibles,  petrol,  various  hydrocarbons, 
alcohol,  producer  gas,  furnace  gases,  etc.,  direct  combustion 
is  advantageous.  It  permits  the  avoidance  of  many  important 
losses,  and  removes  many  operative  objections  and  dangers. 

The  utilization  of  blast-furnace  gases,  coke-oven  gases, 
etc.,  presents  in  itself  an  important  field  for  the  gas  turbine, 
which  may  well  replace  the  bulky  engines  now  in  use. 

The  gas  turbine  also  appears  to  be  as  well  adapted  to  the 
driving  of  dynamos  and  alternators  as  is  the  steam  turbine. 
The  same  is  true  as  regards  the  propulsion  of  ships. 

It  is  also  possible  that  the  development  of  the  gas  tur- 
bine will  permit  the  realization  of  motors  of  excessively  light 
weight  for  use  in  aerial  navigation. 

We  may  thus  predict  for  the  gas  turbine  an  extensive 
field  of  application,  and  it  is  altogether  possible  that 
practical  experience  will  enable  many  special  advantages 
to  be  developed,  as  so  often  has  been  the  case  in  connection 
with  the  appearance  of  new  and  improved  appliances. 


CHAPTER  IV. 

THE  DISCUSSION  BEFORE  THE  FRENCH  SOCIETY  OF  CIVIL 
ENGINEERS.— (Continued.) 

THE  paper  of  M.  Sekutowicz,  which  has  been  given  in  full 
in  the  preceding  chapter,  naturally  elicited  an  animated  dis- 
cussion which  will  be  found  in  the  memoirs  of  the  Societe.* 

M.  Rene  Armengaud  gave  an  account  of  his  own  experi- 
mental researches  made  at  St.  Denis  in  connection  with  M. 
Lemale,  and  these  will  be  discussed  at  length  in  a  following 
chapter. 

M.  Jean  Rey  discussed  especially  the  problem  of  the  com- 
pressor, showing  the  importance  of  the  development  of  a  satis- 
factory rotary  or  turbine  compressor.  To  use  a  reciprocating 
compressor  would  be  to  deprive  the  gas  turbine  of  most  of 
the  advantages  to  be  gained  over  the  ordinary  gas  engine. 

Passing  to  the  turbine  compressor,  M.  Rey  described  the 
multiple  turbine  compressor  of  Rateau,  as  installed  in  the 
mines  at  Bethune,  and  constructed  by  Sautter,  Harle  &  Co. 

In  this  machine  there  are  four  sets  of  turbine  wheels 
arranged  in  series,  revolving  at  4500  revolutions  per 
minute.  The  first  set  draws  in  the  air  at  atmospheric 
pressure,  and  raises  it  to  1.7  kg.  per  square  centimetre  abso- 
lute (24  pounds  per  square  inch).  The  second  set  increases 
the  pressure  to  2.9  kg.  (41  pounds);  the  third  to  4.9  kg.,  and 
the  fourth  to  a  final  pressure  of  7.2  kilogrammes  absolute 
per  square  centimetre  (102.4  pounds  per  square  inch). 

This  compressor  has  a  capacity  of  1  kilogramme  of  free 
air  per  second;  it  has  attained  a  capacity  of  1.25  kilogramme, 
and  the  pressure  has  been  pushed  up  to  8.2  kilogrammes 
absolute,  or  7.2  kilogrammes  above  atmospheric  pressure,  or 

*  Memoires  et  Compte  Rendu  des  Travaux  de  la  Societe  des  Ingenieurs 
Civils  de  France:  May,  1906.  Mm.  Armengaud,  Rey,  Hart,  Letombe,  Bochet, 
Deschamps. 

219 


220  THE   GAS   TURBINE. 

about  100  pounds  per  square  inch  over  and  above  atmos- 
pheric pressure. 

The  efficiencies  of  the  various  sections  differ,  attaining  70 
per  cent,  for  the  first,  and  55  per  cent,  for  the  fourth;  the 
mean  efficiency  of  the  entire  machine  being  about  63  per  cent. 

M.  Rey  does  not  consider  it  practicable  to  construct  such 
compressors  to  produce  pressures  of  30,  40,  or  50  kilogrammes 
per  square  centimetre,  as  required  by  M,  Sekutowicz,  so 
that  it  would  be  necessary  to  supplement  it  by  a  small  piston 
compressor. 

M.  Rey  computes  the  practical  efficiency  of  a  turbine 
by  calculating  the  energy  absorbed  in  the  compression  of  1 
kilogramme  of  air,  as  well  as  the  energy  developed  by  a 
kilogramme  of  burned  gases  upon  the  wheel,  and  his  compu- 
tation shows  these  two  amounts  to  be  about  equal,  so  that 
there  would  be  no  power  available  for  external  use.  This, 
however,  hardly  seems  correct,  since  we  have  the  energy 
furnished  by  the  burned  fuel  added  to  that  contained  in  the 
compressed  air,  and  their  sum  should  be  considered.  The 
practical  operation  of  the  turbine  of  Armengaud  and  Lemale 
also  furnishes  a  refutation  of  the  theoretical  calculations 
of  M.  Rey,  since  it  has  developed  500  horse-power,  only 
about  one-half  of  which  was  required  to  operate  the  Rateau 
compressor  by  which  it  was  served. 

M.  G.  Hart  called  attention  to  the  practical  structural 
difficulties  attending  the  realization  of  an  operative  gas  tur- 
bine. In  addition  to  the  question  of  an  efficient  rotary 
compressor  for  high  pressures,  there  are  several  other  ques- 
tions to  be  settled.  Among  these  he  emphasized  the  high 
rotative  speeds  to  be  realized,  these  bringing  centrifugal 
stresses  upon  the  materials  of  which  the  resistance  would 
necessarily  be  reduced  by  the  high  temperatures.  Even 
if  the  difficulties  attending  the  cooling  of  the  rotating  parts 
are  successfully  overcome,  there  will  be  expansion  and  con- 
traction stresses  which  must  be  taken  into  account. 


THE   GAS   TURBINE. 221 

As  regards  the  combustion  chamber  there  are  several 
questions  involved  in  its  successful  construction,  although 
M.  Armengaud  appeared  to  have  adopted  an  effective  design. 
M.  Hart  suggested  that  several  combustion  chambers 
arranged  in  series  might  be  found  more  advantageous  than 
a  single  one  of  larger  size,  especially  in  connection  with  speed 
regulation  for  light  loads. 

The  practical  solution  of  the  gas  turbine  question, 
according  to  M.  Hart,  appears  to  lie  in  the  perfection  of  a 
number  of  details,  a  result  attainable  only  by  means  of  ex- 
haustive experimental  investigations. 

M.  Bochet  called  attention  to  the  fact  that  high  degrees 
of  compression  were  necessary  if  high  thermal  efficiencies 
were  to  be  attained,  citing  the  experience  of  the  Diesel 
motor,  in  which  the  temperature  of  compression  is  sufficient 
to  cause  the  ignition  of  the  combustible.  Such  high  com- 
pressions, however,  are  as  yet  entirely  beyond  the  powers  of 
the  best  turbine  compressors,  a  fact  which  militates  severely 
against  the  success  of  the  gas  turbine  so  far  as  efficiency  is 
concerned. 

M.  L.  Letombe  compared  the  possibilities  of  the  gas  tur- 
bine with  the  achieved  performances  of  the  piston  gas  en- 
gine. He  believed  that  the  steam  turbine  had,  in  some 
cases,  been  found  preferable  to  the  steam  engine  because  of 
its  greater  simplicity,  but  it  seemed  as  if  this  point  could  not 
be  advanced  for  the  gas  turbine,  because  the  latter  machine, 
at  least  so  far  as  developed  at  present,  was  more  complicated 
than  the  reciprocating  gas  engine. 

In  closing  the  discussion,  M.  Sekutowicz  reviewed  the 
criticisms  which  his  paper  had  elicited,  commenting  upon  the 
influence  which  the  variability  in  the  specific  heat  of  gases  at 
very  high  temperatures  might  have  upon  his  computations, 
and  emphasizing  the  desirability  of  submitting  the  doubtful 
points  to  the  test  of  actual  investigation  in  the  mechanical 
laboratory. 


CHAPTER  V. 

ACTUAL  BEHAVIOR  OF  GASES  IN  NOZZLES. 

ONE  of  the  most  essential  elements  in  the  success  of  the 
gas  turbine  lies  in  the  practicability  of  the  conversion  of  the 
original  potential  energy  of  the  gases  into  kinetic  energy  in 
the  nozzle.  The  extent  to  which  this  can  be  accomplished 
is  yet  a  matter  for  discussion. 

Experimental  investigations  upon  the  free  expansion 
of  gases  in  nozzles,  conducted  by  Dr.  Charles  E.  Lucke,  at 
Columbia  University,  appear  to  show  that  the  nozzle  is  a  far 
less  efficient  means  for  the  conversion  of  energy  than  the 
piston  and  cylinder.  Referring  to  experiments  made  upon 
the  expansion  of  compressed  air  to  show  the  extent  of 
temperature  drop,  Dr.  Lucke  says: 

"Holding  a  thermometer  in  the  stream  of  air  issuing  from 
an  open  valve  or  nozzle  on  a  compressed  air  main  will  show, 
for  even  a  pressure  drop  of  100  pounds  per  square  inch,  only 
three  or  four  degrees  temperature  change.  This  also  may 
be  due  to  impact  on  the  thermometer  raising  the  temperature 
of  the  moving  gases  by  bringing  them  to  rest  on  the  bulb; 
but  again  this  will  not  account  for  the  whole  difference  be- 
tween what  is  observed  and  what  would  be  were  this  free 
expansion  equivalent  to  balanced  expansion.  To  eliminate 
the  errors  of  impact  as  much  as  possible,  a  thermal  couple 
stretched  axially  along  the  jet  and  made  of  fine  wire  has 
been  used  by  the  author  for  a  measurement  of  the  tempera- 
ture of  the  air  when  moving  at  the  maximum  velocity.  The 
maximum  temperature  drop  for  air  under  100  pounds  initial 
pressure,  expanding  through  a  steam  turbine  nozzle  into 
atmosphere,  is  only  30  degrees  F.  This  result  is  only  12  per 
cent,  of  the  temperature  drop  that  would  have  resulted  did 
the  air  suffer  balanced  expansion  without  gain  or  loss  of  heat. 

222 


THE   GAS   TURBINE.  223 

"Another  instance  of  the  same  lack  of  equivalence  in  re- 
sults by  free  and  balanced  expansion  is  found  in  the  experi- 
ments of  Tripler  and  Linde  on  the  making  of  liquid  air.  In 
this  work  air  highly  compressed  (2000  to  3000  pounds  per 
square  inch)  is  first  cooled  by  water  and  then  some  of  the 
air  freely  expanded  through  a  hole,  the  discharge  passing 
around  the  pipe  feeding  the  hole.  This  was  intended  to  cool 
the  air  in  the  pipe  lower  than  the  critical  temperature  for 
liquefaction  under  the  high  pressure  used.  The  results 
were  enormously  different  from  the  case  for  balanced  expan- 
sion, the  temperature  drop  through  the  nozzle  being  about 
\  degree  F.  per  atmosphere-pressure  drop,  according  to  one 
report.  More  accurately  the  results  for  the  Linde  process 
are  shown  in  the  following  table,  the  initial  pressure  being 
220  atmospheres. 

Temperature  approaching  the  Actual  temperature  drop 

nozzle.  through  nozzle. 

+  30°  F.  35°  F. 

0°  F.  65°  F. 

—  30°  F.  80°  F. 

—  60°  F.  96°  F. 
-100°  F.  112°  F. 

—150°  F.  135°  F. 

"Unless,  by  an  increase  of  knowledge  of  free  expansion  of 
perfect  gases,  it  becomes  possible  to  produce  results  equiva- 
lent to  those  obtained  with  balanced  expansion,  there  cannot 
be  the  same  amount  of  heat  transformed  into  work  by  the 
gas  turbine  engine  as  by  the  cylinder-and-piston  gas  engine." 
Later  investigations  made  by  Dr.  Lucke  in  operating 
a  De  Laval  steam  turbine  with  compressed  air  gave  interest- 
ing results,  an  abstract  of  which  is  here  given. 

"For  convenience  of  operation  the  air  was  cold  air, 
whereas  in  the  practical  gas  turbine  the  air  would  be  hot 
and  possibly  more  or  less  mixed  with  steam,  or  possibly  no 
air  at  all,  but  carbon  dioxide.  In  any  event,  the  working 


224  THE    GAS   TURBINE. 

fluid  would  be  largely  a  perfect  gas.  The  turbine  used  was 
a  De  Laval  standard  30  horse-power  machine  intended  for 
steam  at  110  pounds  pressure  and  having  six  nozzles.  The 
turbine  wheel  runs  at  20,000  revolutions  per  minute,  and  the 
power  shaft  2000  revolutions.  The  air  used  for  driving 
the  turbine  was  measured  by  a  Westinghouse  metre.  The 
tests  were  run  on  no  load,  because  the  compressor  used  was 
not  sufficiently  large  to  supply  the  amount  of  air  needed  at 
full  load,  or  even  at  full  speed  without  load.  With  each  type 
of  nozzle  three  different  initial  pressures  were  used,  each 
with  a  different  number  of  nozzles.  Readings  were  taken  of 
the  temperature  of  the  air  entering  the  turbine  and  the 
temperature  of  the  air  in  the  exhaust  chamber,  with  the 
corresponding  pressures.  The  nozzles  fitted  to  this  turbine 
in  holes  Numbers  1  and  4  are  110  pounds  pressure  and  25  J 
inches  vacuum;  in  holes  Numbers  3  and  6  for  110  pounds 
pressure  and  26.3  inches  vacuum;  and  in  holes  Numbers  2 
and  5  for  110  pounds  steam  pressure  and  atmospheric 
exhaust.  The  results  of  the  pressure-drop  runs  are  given 
in  the  following  table,  which  also  gives  the  theoretical 
temperature-drop,  assuming  an  adiabatic  expansion  of  air 
between  the  same  pressures. 

"From  this  it  appears  that  the  temperature-drop  realized 
varies  from  4  to  18  per  cent,  of  the  theoretical  or  adiabatic 
temperature-drop.  The  preceding  results  are  given  with  re- 
spect to  speeds  also,  which  varied  from  520  to  1920  revo- 
lutions per  minute.  To  show  according  to  what  law  this 
complete  process  takes  place,  the  exponent  of  the  tempera- 
ture ratio  in  the  equation  between  pressure  ratio  and  tem- 
perature ratio,  which  for  adiabatic  expansion  of  air  is  .29, 
was  determined  and  found  to  lie  between  .1005  and  .0380." 
These  results  obtained  by  Dr.  Lucke  must  be  compared 
with  the  practical  ones  secured  by  the  engineers  of  the 
Societe  des  Turbomoteurs  at  St.  Denis  and  the  experiments 
made  by  M.  Alfred  Barbezat  upon  the  small  experimental 


THE   GAS   TURBINE. 


225 


8<£>COCOCOGOGCGOOOGOOOGOCOGOGCCD?OGOCOCOGOOOOOO?OCOCOCO 
CO  H-»  I— 'COGO^ICOOl-^I<COOfcOCOt— >  tO  GO  CO  H- '  h-»  Ol  I— '^GOCOtO^lCSCOGO 


ClOOlGOtOGOCOGCCCGOrfi.OCOGCOib-'CCtO 


ascoco^co  GO  oc  oo  GO  ox 

OasCni—  '  CO  O5  I—  »  CO  CO  GO 


1 1  Hi  iLLiiiiu  1 1 1 1  jj  n 

;OiOO:i— 'OH- 'OOStOOCOCO 


T3  § 

II 


»-a  |_i  (-1  t—  '  tO         I—  i 

tOOiH-  '^lOCni—  ' 


GOtOOi 


t—  '  CO  4^  h-»  h-  1 


s 


I* 


3 

5'  §* 

•g  ^ 

g  t9 


I  fe1 

II 


I 


O5  GO  CO  'in  CO 


OiOOC/iCnOOOO 


£ 


o 


15 


226  THE   GAS   TURBINE. 

turbine  of  Mm.  Armengaud  and  Lemale  show  a  much 
greater  drop.  It  is  greatly  to  be  desired  that  this  whole 
subject  of  free  expansion  in  nozzles  for  steam,  for  air,  and 
for  mixed  gases,  at  various  temperatures  should  be  thor- 
oughly investigated  experimentally,  and  it  might  well  occupy 
the  efforts  of  some  of  the  highly  equipped  mechanical  and 
physical  laboratories  of  the  technical  schools. 


CHAPTER  VI. 

THE  PRACTICAL  WORK  OF  ARMENGAUD  AND  LEMALE. 

THE  most  complete  account  of  the  Armengaud  and  Le- 
male  turbine,  the  gas  turbine  which,  by  its  practical  perform- 
ances has  done  the  most  to  demonstrate  that  the  gas  tur- 
bine is  a  reality,  and  not  merely  an  academic  discussion,  is 
contained  in  an  article  by  the  late  M.  Rene  Armengaud, 
published  in  Cassier's  Magazine,  and  here  reprinted.* 
M.  Armengaud  reviews  the  principles  of  the  gas  turbine, 
and  describes  some  early  devices,  and  then  proceeds : 

Heat  motors  in  general  service  at  the  present  time  may 
be  grouped  into  the  following  classes : 

1.  Alternating  steam   motors    (reciprocating  steam  en- 
gines). 

2.  Alternating    combustion    motors    (reciprocating    gas 
engines). 

3.  Continuous  steam  motors  (steam  turbines). 

4.  Continuous  combustion  motors  (gas  turbines). 

Of  these  various  machines  the  latest,  and  certainly  the 
least  known,  is  that  which  appears  to  have  a  most  interesting 
future,  the  gas  turbine,  and  it  is  this  which  I  now  propose 
to  discuss. 

A  successful  gas  turbine  aims  to  combine  the  great  advan- 
tages of  the  gas  engine,  including  the  elimination  of  the 
steam  boiler  and  a  high  thermal  efficiency,  with  the  special 
advantages  of  the  steam  turbine,  i.  e.,  simplicity  of  construc- 
tion, lightness,  and  the  greatly  desired  property  of  continu- 
ous motion  in  one  direction,  with  the  accompanying  features 
of  control  and  regulation. 

The  various  plans  which  have  been  discussed  for  the  de- 

*  The  Gas  Turbine.  Practical  results  with  actual  operative  machines  in 
France.  By  Rene  Armengaud,  Cassier's  Magazine,  January,  1907. 

227 


228 


THE   GAS   TURBINE. 


sign  of  the  gas  turbine  may  be  divided  into  three  groups :  hot- 
air  turbines,  explosion  turbines,  and  combustion  turbines. 
So  far  as  the  first  group  is  concerned,  I  have  not  attempted 
to  make  any  investigations  in  this  direction,  believing  this 
system  to  offer  few  advantages.  The  only  machine  of  this 
kind  of  which  I  have  any  knowledge  is  that  of  Dr.  Stolze,  of 
Charlottenburg,  of  which  the  following  description  is  ab- 
stracted from  his  patents.  Air  is  compressed  by  means  of  a 
helicoidial  compressor  to  about  1J  atmospheres.  The  air, 
after  having  circulated  about  a  furnace,  expands,  and  is  then 
passed  through  a  turbine  attached  to  the  same  shaft  as  the 
compressor. 


FIG.  74.-<-General  arrangement  of  explosion  gas  turbine. 

In  the  case  of  the  second  group,  the  explosion  turbines, 
the  air  compressor  is  eliminated  or  greatly  simplified.  The 
explosive  mixture  is  formed  in  the  same  chamber  in  which 
it  is  ignited,  being  either  at  atmospheric  pressure  or  slightly 
above,  and  by  its  expansion,  consequent  upon  the  explosion, 
it  acts  upon  the  turbine  wheel.  The  principle  of  such  a 
machine  is  shown  in  Fig.  74.  The  explosion  chamber  is 
.closed  at  the  back  by  a  valve  A  held  to  its  seat  by  a  light 
spring  B,  the  chamber  having  an  expanding  nozzle  opening 
at  C.  The  gas  enters  at  small  openings,  as  at  E  under  the 
seat  of  the  valve,  and  the  air  is  admitted  at  F,  the  mixture 
being  ignited  electrically  at  H,  and  discharged  through  tho 


THE   GAS   TURBINE. 


229 


nozzle  C  upon  the  buckets  of  the  turbine  wheel  T.  The  dis- 
charged gases  pass  through  an  induced  current  nozzle  G  which 
acts  to  reduce  the  temperature  of  the  issuing  gases  and  lower 
the  velocity  of  the  jet  as  it  acts  upon  the  turbine  wheel. 

Such  an  apparatus,  when  properly  proportioned,  will  make 
about  three  explosions  per  second,  and  will  continue  to  run 
automatically  after  it  has  once  been  started. 


o  0.05-  o.i  o 

FIG.  75. — Explosion  turbine  diagram. 


Various  theories  have  been  advanced  to  explain  the  ac- 
tion of  this  device.  The  most  satisfactory  explanation  of 
the  periodic  action  is  that  of  the  sudden  cooling  of  the  cham- 
ber after  each  explosion.  This  cooling  causes  a  correspond- 
ing drop  in  the  pressure,  followed  by  the  opening  of  the  valve 
A  and  the  aspiration  of  the  air  and  gas,  and  as  soon  as  the 
explosive  mixture  reaches  the  igniter  a  fresh  explosion 
follows.  In  Fig.  75,  the  variations  in  pressure  in  the  cham- 
ber are  shown  as  a  function  of  time.  The  maximum  effective 
pressure  ranges  from  2  to  3  kilogrammes  per  square  centi- 
metre, or  about  30  to  45  pounds  per  square  inch,  although 
the  theoretical  pressure  in  such  an  open  vessel  should 
reach  4  kilogrammes,  so  that  the  mixture  of  the  gas  and  air 
is  probably  imperfect. 

Theoretically,  the  explosion  turbine  should  have  a  certain 
thermal  advantage  over  the  corresponding  cycle  for  a  com- 
bustion turbine.  The  specific  heat  at  constant  volume  be- 


230 


THE   GAS   TURBINE. 


ing  lower  than  the  specific  heat  at  constant  pressure,  the 
same  quantity  of  heat  acting  upon  the  same  mass  of  gas 
should  produce  a  higher  temperature  after  the  explosion 
than  after  a  combustion.  Since,  according  to  the  principle 
of  Carnot,  the  efficiency  is  proportional  to  the  maximum 
temperature  of  the  fluid  before  expansion,  the  explosion  tur- 
bine should  be  more  efficient  than  the  combustion  turbine. 
Unfortunately  the  high  velocities  of  discharge  of  the  gases, 
and  the  variations  in  the  pressure,  render  it  impracticable  to 
realize  more  than  a  small  fraction  of  the  energy  of  the  jet 
upon  the  wheel.  Thus,  the  theoretical  efficiency  of  such  a 


FIG.  76. — Combustion  gas  turbine.    A,  combustion  chamber.    B,  fuel  inlet.    C,  fuel  sprayer. 
E,  expansion  nozzle.     F,  turbine. 


machine  should  be  about  16  per  cent.,  while  the  actual  per- 
formance does  not  exceed  3  to  4  per  cent.  In  addition  to 
this  defect  there  are  operative  difficulties  with  the  springs 
and  valves,  and  the  frequent  breakages  and  delicate  adjust- 
ments have  rendered  experiments  to  improve  the  apparatus 
unsatisfactory. 

There  remains,  then,  the  combustion  turbine,  which,  in 
spite  of  the  necessity  for  an  air  compressor,  is  greatly 
to  be  preferred,  especially  for  large  units.  This  machine 
consists  in  principle  of  a  combustion  chamber  A  Fig.  76. 
supplied  by  a  continuous  current  of  compressed  air,  and  also 
by  a  continuous  supply  of  liquid  fuel,  gasoline,  petroleum, 


THE   GAS   TURBINE. 231 

or  the  like,  under  pressure  through  a  tube  B,  the  mixture 
being  ignited  at  the  start  by  a  platinum  wire  C,  the  combus- 
tion developing  a  constant  temperature  of  about  1300  de- 
grees C.  in  the  chamber  D.  The  fluid  products  of  combustion 
are  then  continuously  discharged  through  a  nozzle  E,  upon 
the  buckets  of  the  turbine  wheel  F. 

The  principal  defect  in  this  apparatus  in  comparison  with 
the  reciprocating  gas  engine  is  the  necessity  for  a  separate 
air  compressor,  instead  of  having  the  compression  of  the 
charge  effected  in  the  motor  itself.  This  defect  is  partially 
remedied  by  the  diminution  of  the  losses  through  the  walls, 
and  by  the  possibility  of  an  expansion  which  is  practically 

C     B 


FIG.  77. — Diagram  for  combustion  turbine. 

adiabatic.  The  combustion  is  also  more  complete  than  is 
possible  in  a  working  cylinder,  and  all  the  products  of  com- 
bustion are  utilized. 

The  action  of  a  combustion  turbine  is  graphically  shown 
in  Fig.  77.  In  this  diagram  the  area  OABC  represents  the 
energy  required  for  the  air  compressor.  The  combustion  of 
the  liquid  fuel  increases  the  volume  from  CB  to  CD.  If  any 
vapor  of  water  is  introduced,  this  volume  will  be  diminished 
from  CD  to  CDl}  while  at  the  same  time  its  mass  increases 
the  volume  of  CD^  to  CE.  The  effective  energy  exerted  by 
the  turbine  will  be  represented  by  the  area  OFEC  and  that 
available  after  the  deduction  of  the  work  of  compression  will 
be  AFEB. 


232  THE    GAS   TURBINE. 

In  endeavoring  to  produce  such  a  cycle  in  an  actual 
working  machine,  the  following  practical  difficulties  must 
be  overcome: 

A  gaseous  fluid  moving  at  a  high  velocity  must  be  kept 
constantly  ignited,  by  a  device  which  must  not  be  affected 
by  the  high  temperature  of  the  combustion  chamber. 

The  mixture  of  the  combustible  and  the  air  must  be  made 
as  perfect  as  possible. 

The  injurious  action  of  the  gaseous  products  at  a  high 
temperature  upon  the  parts  of  the  apparatus,  and  upon  the 
turbine  wheel  itself,  must  be  prevented. 

For  three  years  a  machine  complying  with  these  condi- 
tions has  been  running  successfully  in  the  shops  of  the  So- 
ciete  des  Turbomoteurs  at  Paris,  this  apparatus  being  the 
Armengaud-Lemale  turbine,  of  which  some  further  descrip- 
tion will  be  given. 

The  original  machine  was  made  from  a  De  Laval  steam 
turbine  of  25  horse-power,  arranged  to  be  operated  with 
compressed  air  instead  of  steam.  The  air  was  supplied  at 
any  desired  pressure  from  a  high  speed  compressor,  of  which 
the  efficiency  had  been  closely  determined,  while  prolonga- 
tions of  the  pipe  which  connected  the  compressor  to  the  tur- 
bine formed  the  combustion  chamber.  At  the  entrance  of 
each  chamber  the  gasoline,  mixed  with  the  air,  was  ignited 
by  an  incandescent  platinum  wire,  this  ignition  being  neces- 
sary only  at  the  starting  of  the  operation,  the  combustion 
being  maintained  continuously  thereafter  at  constant  pres- 
sure. The  combustion  chambers  were  lined  with  refractory 
material,  and  a  temperature  of  about  1800  degrees  C.  was 
produced.  In  order  to  reduce  the  temperature  to  practical 
limits  the  chamber  was  cooled  by  the  introduction  of  vapor 
of  water  generated  in  a  spiral  imbedded  in  a  portion  of 
the  combustion  chamber.  The  steam  thus  produced  was 
allowed  to  mingle  with  the  gases  of  combustion  before  expan- 
sion in  such  proportion  that  the  temperature  of  the  mixture 
was  about  400  degrees  C. 


FIG.  89.— The  30  horse-power  experimental  gas  turbine  of  the  Societe  des  Turbomoteurs. 


FIG.  90. — The  300  horse-power  gas  turbine  of  Armengaud  and  Lemale  connected  to  th 
Rateau  polycellular  turbine  compressor. 


THE   GAS   TURBINE.  233 

Although  this  apparatus  was  necessarily  crude  and  not 
proportioned  in  such  a  manner  as  to  give  the  best  results,  it 
enabled  the  conditions  essential  for  a  good  efficiency  to  be 
determined. 

Among  the  practical  points  thus  determined  were  proofs 
that  it  was  entirely  possible  to  maintain  the  combustion 
chamber,  turbine  wheel,  and  fuel  pulverizer  in  operative  con- 
dition. The  experiments  also  showed  it  to  be  practicable  to 
maintain  a  very  high  temperature  continuously  in  the  actual 
combustion  chamber,  and,  by  means  of  this  high  heat  to 
secure  a  perfect  combustion  of  any  combustible.  The  work 
of  compression  having  been  carefully  ascertained  for  the  pur- 
pose of  deducting  it  from  the  brake  power  developed  by 
the  entire  machine,  it  appeared  that  even  with  this  imperfect 
apparatus  the  total  power  was  about  double  that  necessary 
to  drive  the  compressor.  This  result  was  attained  with  a 
pressure  of  about  10  kilogrammes  per  square  centimetre,  and 
a  temperature  of  400  degrees  C.  at  the  exhaust. 

As  has  already  been  said,  the  excessively  high  tempera- 
tures developed  were  reduced  in  the  earlier  experiments  by 
mixing  a  certain  quantity  of  steam  with  the  gases  of  com- 
bustion before  expansion.  This  method,  while  accomplish- 
ing the  result  desired,  also  acted  to  lower  the  efficiency  of  the 
turbine,  doubtless  because  of  the  latent  heat  of  vaporization 
lost  in  the  exhaust.  In  the  diagram,  (Fig.  78)  the  curves 
show  the  manner  in  which  the  economical  performance  of  this 
machine  varied,  represented  as  a  function  of  the  upper  pres- 
sure and  of  the  temperature  of  the  exhaust  gases.  This  dia- 
gram has  been  computed  upon  a  basis  of  60  per  cent, 
efficiency  of  the  turbine  wheel,  and  80  per  cent,  of  the  com- 
pressor. For  example,  with  a  pressure  of  30  kilogrammes 
per  square  centimetre,  and  an  exhaust  temperature  of  450 
degrees  C.,  an  efficiency  of  18  per  cent,  is  obtained. 

It  thus  appears  that  the  efficiency  depends  both  upon  the 
pressure  and  upon  the  temperature  of  the  exhaust  gases. 


234 


THE   GAS   TURBINE. 


In  order,  therefore,  to  obtain  the  best  efficiency  it  is  neces- 
sary to  prevent  cooling  the  gases  before  expansion,  either  by 
introducing  steam  into  the  combustion  chamber,  or  other- 
wise, and  to  effect  the  greatest  possible  reduction  in  temper- 
ature in  the  expansion  alone. 

The  difficulties  accompanying  the  high  temperatures 
may  be  met  in  the  case  of  the  combustion  chamber  and  other 
fixed  parts  by  the  use  of  a  water  jacket  and  by  the  employ- 

t      1750'C 
t 


SCO 


iSo 


I       5        to  20  30 

FIG.  78. — Gas  turbine  economy  curves. 

ment  of  a  refractory  lining,  and  the  real  difficulties  are 
reached  only  when  it  becomes  necessary  to  provide  for  the 
effect  of  the  highly  heated  fluid  upon  the  rotating  metallic 
wheel,  already  weakened  by  the  heavy  centrifugal  stresses 
to  which  it  is  necessarily  subjected. 

The  most  practical  way  of  keeping  the  turbine  wheel  cool 
is  to  follow  the  jet  of  hot  gases  by  another  jet  of  a  low  tem- 
perature so  that  the  buckets  of  the  wheel  pass  successively 
through  alternate  hot  and  cool  zones,  the  average  tempera- 


THE   GAS   TURBINE. 


235 


ture  of  the  two  jets  being  sufficiently  low  to  prevent  injury  to 
the  metal.  The  low  temperature  jet  found  most  practicable 
is  that  of  low  pressure  steam,  and  this  is  readily  provided 
from  the  water  jacket  and  from  a  device  arranged  as  a  re- 
generator in  connection  with  the  exhaust  gases. 

This  arrangement,  shown  in  Fig.  79,  gives  a  general  idea 
of  the  system.  The  air  from  the  compressor  enters  at  D  and 
is  mixed  with  the  liquid  fuel  in  the  concentric  nozzle  EE  and 


»^ 


Water 


FIG.  79. — Mixed  gas  and  steam  turbine.  Air  enters  at  D,  fuel  at  F,  the  ignition  is  made 
at  G.  The  combustion  chamber  A  is  lined  with  carborundum.  The  nozzle  H  is  water- 
jacketed,  and  the  hot  water  passes  to  the  steam  generator  L,  which  is  heated  by  the  exhaust 
gases  from  the  turbine.  The  steam  acts  to  propel  and  cool  the  wheel  by  the  nozzle  M . 

ignited  by  the  platinum  wire  at  G.  The  combustion  takes 
place  continuously  at  constant  pressure  in  the  chamber  A, 
and  the  products  of  combustion  are  discharged  through  the 
expansion  nozzle  H  upon  the  buckets  of  the  turbine  wheel  1. 
The  nozzle  itself  is  protected  by  a  water  jacket  C,  the  water 
leaving  the  jacket  at  K.  On  the  other  side  of  the  wheel 
there  is  arranged  a  sort  of  flash  steam  generator  L,  this 
being  composed  of  a  serpentine  pipe  of  continually  increasing 
diameter,  the  water  entering  the  small  end  at  K,  this  en- 


236 


THE   GAS   TURBINE. 


trance  forming  a  part  of  the  discharge  pipe  from  the  water 
jacket  of  the  nozzle  H.  The  steam  generator  L  is  placed  in 
the  path  of  the  exhaust  gases  leaving  the  turbine  wheel, 
and  these  highly  heated  gases  furnish  the  heat  necessary  to 
convert  the  water  into  steam,  the  vapor  thus  produced 
being  discharged  through  the  nozzle  M  upon  the  turbine 
wheel,  thus  acting  both  to  aid  in  the  propulsion  and  to 
form  a  zone  of  comparatively  low  temperature  to  abstract 
heat  from  the  wheel.  By  this  arrangement  it  is  possible  to 
reduce  the  temperature  of  the  wheel  to  practicable  limits, 
provided  the  temperature  of  the  exhaust  gases  is  sufficiently 
high  to  produce  enough  steam.  That  is,  the  expansion  of 


FIG.  80.— The  Lemale  combustion  chamber. 

the  gases  in  the  nozzle  must  not  lower  their  pressure  and 
temperature  so  far  as  to  keep  down  the  volume  of  steam  too 
low.  In  such  case  it  is  always  practicable  to  admit  a  small 
quantity  of  superheated  steam  into  the  combustion  chamber 
and  thus  obtain  the  required  temperature  without  affecting 
the  efficiency  of  the  machine  too  much. 

The  general  heat  balance  of  a  gas  turbine  using  a  steam 
regenerator  according  to  the  above  plan  is  shown  in  Fig.  81, 
in  which  the  total  -quantity  of  energy  produced  by  the  fuel 
is  represented  by  the  dimension  X,  and  the  various  losses 
indicated  by  the  cross  hatched  portions  in  the  body  of  the 
diagram.  The  efficiency  of  the  machine  is  then  obtained 
as  the  ratio  Y :  X,  Y  being  composed  of  two  parts,  one  of 


THE   GAS   TURBINE. 


237 


which  is  obtained  from  the  action  of  the  gases  upon  the  wheel 
and  the  other  by  the  steam. 

In  this  arrangement  the  expansion  of  the  gases  and  the 
steam  occur  in  parallel,  so  to  speak,  this  being  clearly 
indicated  in  the  diagram.  For  constructive  reasons,  how- 
ever, it  is  found  convenient  to  adopt  the  previous  system, 
the  steam  produced  in  the  regenerator  being  delivered  into 


FIG.  81. — Heat  balance  diagram  for  mixed  gas  turbine.  I,  total  energy  developed  by 
the  combustion  of  the  fuel.  II,  kinetic  energy  available  at  the  discharge  of  the  nozzle. 
Ill,  energy  developed  on  the  turbine  wheel.  IV,  energy  developed  less  the  power  required 
to  drive  the  compressor.  V,  energy  recovered  in  the  steam.  VI,  energy  available  in  the 
expanding  steam.  VII,  energy  developed  by  the  steam  on  the  wheel.  X,  total  energy  con- 
tained in  the  fuel.  Y,  total  energy  produced  in  indicated  work,  a,  Radiation  losses  from 
the  combustion  chamber,  b,  Loss  in  the  nozzle,  c,  Compressor  losses,  d,  Theoretical 
work  of  compression,  e,  Radiation  losses  from  the  turbine.  /,  Losses  in  the  exhaust 
steam,  g,  Losses  in  the  exhaust  gases. 

the  same  nozzle  as  that  used  for  the  gases,  and  this  plan  has 
been  adopted  in  our  most  recent  turbine,  even  at  some  re- 
duction in  the  thermal  efficiency. 

This  machine,  shown  in  several  views,  is  of  the  same 
general  type  as  the  Curtis  steam  turbine,  and  is  capable  of 
delivering  from  400  to  800  h.  p.,  according  to  the  compressor 
capacity  utilized.  The  turbine  is  operated  at  4000  revolu- 


238  THE   GAS   TURBINE. 

tions  per  minute,  and  the  speed  regulation  is  effected  by  a 
throttling  valve  in  the  air  admission  pipe  for  small  speed  var- 
iations, and  by  a  change  in  the  fuel  supply  for  larger  changes, 
the  regulating  valves  being  controlled  by  a  Hartung  gover- 
nor. There  are  three  pumps  attached  to  the  machine,  one 
the  air  compressor,  another  for  the  fuel  supply,  and  the 
third  for  the  water. 

The  combustion  chamber  is  made  of  cast  iron,  lined  with 
carborundum,  the  cast  iron  being  protected  with  a  water 
jacket.  An  elastic  non-conducting  lining  is  placed  between 
the  carborundum  and  the  outer  shell,  this  providing  a  bed- 
ding for  the  carborundum  and  also  permitting  a  slight  move- 
ment for  differences  in  expansion  and  contraction.  The 
extremity  of  the  chamber  and  the  nozzles  are  surrounded 
by  a  jacket  space  in  which  the  water  and  steam  circulate, 
the  nozzles  being  of  the  expanding  type  similar  to  those  of 
the  De  Laval  steam  turbine,  although  the  expansion  is 
completed  in  a  shorter  time.  It  is  necessary  that  the  expan- 
sion should  be  effected  in  a  single  operation  in  order  that  the 
temperature  be  sufficiently  reduced  before  the  gases  reach 
the  wheel. 

The  gasoline  or  other  liquid  fuel  is  delivered  into  the 
combustion  chamber  through  a  pulverizer,  or  atomizer,  the 
construction  of  which  is  shown  in  Fig.  86.  This  is  arranged 
with  a  reverse  annular  opening  B  delivering  the  fuel  back- 
ward against  the  incoming  stream  of  air,  the  angle  causing 
the  gasoline  to  form  a  sort  of  cone  of  minute  particles,  these 
becoming  ignited  as  soon  as  their  decreasing  velocity  per- 
mits. The  preheating  of  the  fuel  also  riders  the  ignition 
easy.  The  atomizer  is  protected  against  the  intense  radiant 
heat  of  the  chamber  wall  by  the  current  of  air  with  which  it 
is  continually  surrounded.  The  igniting  coil  of  platinum 
wire  D  is  protected  by  a  steel  cap  (7,  the  electric  current 
entering  by  the  central  insulated  rod  E,  the  circuit  being 
completed  through  the  machine  itself.  A  pressure  of  2 


FIG.  82. — The  Armengaud  and  Lemale  gas  turbine.    A  view  of  the  500  horse-power  turbine 
in  the  experimental  laboratory  at  St.  Denis. 


FIG.  83.— The  Armengaud   and   Lemale  gas  turbine.    This  view  and  the  preceding  one 
show  the  wheel  casing,  governor,  and  general  arrangement. 


FIG.  84. — The  Armengaud   and   Lemale  gas  turbine.    This  view  shows  the   combustion 
chamber,  air  and  fuel  inlets  and  connections. 


FIG.  85. — The  Armengaud  and  Lemale  gas  turbine.     Another  view  of  the  combustion 
chamber,  with  air  and  fuel  connections. 


THE   GAS   TURBINE. 


239 


volts  is  found  sufficient  to  render  the  platinum  wire  incandes- 
cent. The  atomizer  is  inserted  into  the  combustion  cham- 
ber in  such  a  manner  that  it  can  readily  be  removed  for  in- 
spection and  cleaning,  this  operation  also  giving  complete 
access  to  the  chamber  itself. 

The  turbine  wheel  is  arranged  to  be  cooled  by  water  cir- 
culation as  shown  in  Fig.  87,  this  representing  a  section  of 
the  rim  and  a  portion  of  the  disc.  A  and  B  are  circular 
channels  in  the  body  of  the  rim,  these  being  supplied  with 
water  by  radial  passages  as  at  E.  Small  passages  also  per- 
mit the  water  to  enter  into  each  blade  of  the  turbine  and  the 


FIG.  86. — Section  of  pulverizer  and  igniter. 

difference  in  specific  gravity  between  the  hot  and  cold  water 
is  found  to  make  an  automatic  circulation,  in  connection  with 
the  centrifugal  force  due  to  the  high  velocity  of  rotation. 

The  air  supply  for  the  turbine  is  furnished  by  a  polycel- 
lular  rotary  compressor  of  the  Rateau  system.  This  impor- 
tant adjunct  to  the  gas  turbine,  shown  in  Fig.  88,  is  composed 
of  a  number  of  turbine  blowers  arranged  in  series  and  espe- 
cially designed  to  be  operated  at  very  high  rotative  speeds, 
so  that  it  may  be  directly  connected  to  the  gas  turbine. 

The  importance  of  the  compressor  is  second  only  to  that  of 
the  turbine  itself,  since  it  is  of  little  value  to  possess  a  rotary 


240 


THE   GAS   TURBINE. 


combustion  motor  if  a  reciprocating  compressor  is  a  necessary 
auxiliary.  It  is  on  this  ground,  more  than  almost  any  other, 
that  the  design  of  a  successful  gas  turbine  has  been  consid- 
ered problematical,  and  here,  as  in  many  other  cases  in  the 


FIG.  87. — Section  of  wheel  of  gas  turbine,  showing  passages  for  cool  ing- water. 

history  of  the  development  of  a  device,  the  progress  of  other 
departments  of  work  becomes  essential  to  complete  success. 
The  work  of  M.  Rateau  in  the  improvement  of  the  steam 
turbine  is  well  known,  and  by  the  application  of  the  expe- 
rience thus  gained,  a  machine  for  the  supply  of  compressed 


-II 


II 
n 


|t 

l! 

t-  O 


THE   GAS   TURBINE.  241 

air  to  the  gas  turbine  has  been  produced,  involving  only  ro- 
tary motion,  and  thus  capable  of  being  driven  directly  by  the 
turbine,  and  having  an  efficiency  sufficiently  high  to  permit 
a  good  performance  of  the  combined  apparatus. 

The  Rateau  compressor  is  practically  a  reversal  of  the 
steam  turbine,  and  is  composed  of  a  number  of  elements 
connected  in  series,  so  that  the  pressure  is  cumulative,  the 
action  being  similar  to  that  of  the  multiple  centrifugal 
pumps  which  have  been  employed  with  such  success  for 
delivering  water  against  high  heads. 

Each  element  of  this  compressor  consists  of  two  parts, 
the  revolving  wheel  and  the  diffuser.  The  diffuser  is  ar- 
ranged to  provide  discharge  passages  for  the  air,  having 
gradually  increasing  section  for  the  flow,  in  order  that  the 
velocity  of  the  air  as  it  leaves  the  wheel  may  be  reduced 
with  the  least  possible  loss,  the  kinetic  energy  being  con- 
verted into  pressure.  The  length  of  the  machine  is  such  that 
intermediate  bearings  have  been  introduced  to  provide  sup- 
port and  stiffness  to  the  rotating  parts,  and  the  whole  design 
of  the  compressor  has  been  so  carefully  worked  out  that  an 
efficiency  of  65  per  cent,  has  been  already  attained,  and  pres- 
ent experiments  indicate  that  this  performance  will  be  sur- 
passed. 

In  Fig.  88  a  Rateau  compressor  of  three  sections  is  shown, 
but  larger  machines  have  been  constructed,  and  the  pressures 
attained  naturally  depend  upon  the  number  of  sections. 
Experiments  have  shown  that  in  the  first  section  the  air  is 
compressed  to  1.7  kilogrammes  per  square  centimetre,  or 
about  24  pounds  per  square  inch,  absolute,  the  succeeding 
pressures  being  2.9  kilogrammes,  4.9  kilogrammes,  and  7.2 
kilogrammes  per  square  centimetre,  the  latter  corresponding 
to  112  pounds  per  square  inch  above  vacuum. 

In  a  subsequent  issue  of  Cassier's  Magazine,*  an  article 
was  published  containing  a  communication  from  M.  Alfred 

*  Cassier's  Magazine,  April,  1908. 
16 


242  THE   GAS   TURBINE. 

Barbezat,  who  had  been  associated  with  M.  Rene  Armen- 
gaud,  and  who  continued  in  the  work  after  the  death  of  the 
latter. 

M.  Barbezat  reviewed  the  early  work  of  M.  Armen- 
gaud,  and  then  described  the  later  progress  as  follows: 

The  general  principle  of  the  machine  involves  the  delivery 
of  air  under  pressure  into  a  pear-shaped  chamber  lined  with 
refractory  material  and  provided  with  an  expanding  nozzle 
through  which  a  uniform  flow  of  gases  can  be  delivered  upon 
the  blades  of  the  wheel.  In  the  centre  of  the  air  nozzle  there 
is  arranged  an  axial  tube,  with  a  pulverizer  at  the  inner  end, 
through  which  the  fuel,  in  the  form  of  gasoline,  or  similar 
liquid  hydrocarbon,  is  forced  into  the  chamber.  The  electric 
sparking  device  enables  the  fuel  to  be  ignited  on  starting, 
after  which  the  high  temperature  of  the  chamber  maintains 
the  combustion  indefinitely.  The  high  temperature  pro- 
duced by  the  combustion  greatly  increases  the  volume  of  the 
air,  and  this,  together  with  the  gaseous  products  of  the  com- 
bustion of  the  fuel,  flows  at  a  high  velocity  through  the  ex- 
panding nozzle  upon  the  blades  of  the  wheel. 

In  dealing  with  such  high  temperatures,  the  temperature 
of  the  combustion  being  about  1800  degrees  C.,  the  best  re- 
fractory lining  for  the  combustion  chamber  has  been  found  to 
be  carborundum,  this  being  a  product  of  the  electric  furnace, 
and  thus  having  already  sustained  even  higher  temperature 
than  those  in  the  turbine  combustion  chamber.  An  elastic 
backing  of  asbestos  provides  for  the  expansion  of  the  carbor- 
undum lining,  and  the  nozzle  through  which  the  gases  are 
discharged  upon  the  wheel  is  also  made  of  carborundum. 

In  addition  to  the  provision  of  a  refractory  lining,  it  has 
been  found  necessary  to  surround  the  combustion  chamber 
with  a  water  jacket  in  the  form  of  a  coil  of  pipe  imbedded 
in  the  metal  of  the  chamber  walls,  much  in  the  same  manner 
as  such  coils  are  used  in  the  tuyeres  of  blast  furnaces,  and 
the  circulation  of  the  water  in  the  coils  aids  in  keeping  the 


THE   GAS   TURBINE. 243 

temperature  of  the  combustion  chamber  walls  within  practi- 
cable limits. 

After  the  water  has  circulated  in  the  jacket  tube  it  is 
delivered,  through  small  holes,  into  the  gases  just  before 
they  enter  the  nozzle,  and  is  there  converted  into  steam, 
this  acting  both  to  lower  the  temperature  of  the  issuing  gases 
to  a  point  where  they  will  not  injure  the  blades  of  the  tur- 
bine, and  also  itself  being  discharged  upon  the  wheel  with 
the  gases  and  forming  a  part  of  the  jet,  which  is  thus  com- 
posed of  mingled  gas,  steam,  and  highly  heated  air. 

In  order  to  obtain  the  desired  result  of  a  machine  involv- 
ing only  rotary  motion,  it  is  necessary  that  the  compressed 
air  by  which  the  combustion  chamber  is  fed  should  be  pro- 
duced, not  by  a  reciprocating  piston  compressor,  but  by 
some  form  of  rotary  machine,  preferably  so  arranged 
that  it  can  be  coupled  directly  to  the  turbine  itself.  This 
means  that  the  complete  gas  turbine  must  also  include  a 
rotary  air  compressor,  and  that  such  a  compressor  must  have 
a  high  efficiency  in  itself,  otherwise  it  will  produce  such  a 
large  proportion  of  negative  work  as  to  detract  materially 
from  the  efficiency  of  the  combined  machine,  even  though 
the  actual  thermal  efficiency  of  the  turbine  be  high. 

After  a  number  of  experiments  upon  single  impeller  tur- 
bine air  compressors,  driven  at  high  rotative  speeds  by  De 
Laval  steam  turbines,  the  services  of  Professor  Rateau  were 
enlisted  in  the  work,  and  a  multiple  turbine  compressor, 
designed  by  him  especially  for  this  work,  was  constructed  at 
the  works  of  Brown,  Boveri  &  Co.,  at  Baden,  Switzerland. 
This  machine  is  arranged  in  three  sections  and  provided  with 
continuous  cooling  circulation,  and,  being  thoroughly  tested, 
was  found  to  be  capable  of  delivering  one  cubic  metre  of  air 
per  second  at  a  pressure  of  6  to  7  atmospheres,  with  an 
efficiency  ranging  between  60  and  70  per  cent. 

The  illustration  (Fig.  90)  shows  the  arrangement  with  this 
compressor  coupled  directly  to  the  large  experimental  tur- 


244  THE   GAS   TURBINE. 

bine  constructed  by  M.  Armengaud,  the  turbine  and  the 
compressor  thus  forming  practically  one  machine. 

In  this  arrangement  the  compressor  was  found  to  absorb 
about  one-half  the  total  power  developed  by  the  turbine,  the 
machine,  when  running  at  about  4000  revolutions  per  minute 
developing  about  300  horse-power  over  and  above  the  nega- 
tive work  absorbed  by  the  compressor.  At  the  present 
time  experiments  are  being  made  upon  the  thermal  efficiency 
of  the  machine,  which  is,  as  yet,  not  as  high  as  that  of  the  re- 
ciprocating gas  engine;  but  these  tests  are  not  yet  completed, 
and  the  results  not  available  for  publication. 

During  the  past  few  months  a  practical  application  of 
this  turbine  has  been  made  in  connection  with  the  operation 
of  submarine  torpedoes. 

It  is  well  known  that  in  certain  types  of  such  machines 
the  motive  power  for  the  brief  period  which  elapses  between 
the  discharge  and  the  contact  with  the  target  is  derived 
from  a  store  of  compressed  air,  and  in  some  such  torpedoes 
the  compressed  air  acts  upon  a  turbine  wheel  similar  to  the 
steam  turbine.  This  principle  has  now  been  extended  to  the 
use  of  the  gas  turbine,  the  compressed  air  from  the  reservoir 
passing  through  a  combustion  chamber  and  the  total 
products  of  combustion  together  with  the  vapor  of  water 
acting  on  the  turbine,  and  its  capacity  thus  increased  over 
that  operated  by  compressed  air  alone. 

The  turbines  made  for  this  purpose  develop  120  horse- 
power at  a  speed  of  1000  revolutions  per  minute,  the 
expansion  ratio  being  8.4.  The  weight  of  the  turbine  alone 
is  73.16  kilogrammes,  or  about  1.3  pounds  per  horse-power. 
Including  the  weight  of  the  reservoir  of  compressed  air, 
together  with  the  petrol  and  water  for  a  discharge  lasting  80 
seconds,  the  total  weight  of  the  whole  apparatus  is  about 
295  kilogrammes,  or  a  little  less  than  2.5  kilogrammes,  or 
5.5  pounds  per  horse-power. 

Although  the  gas  turbine  is,  therefore,  still  in  the  experi- 


THE   GAS   TURBINE. 


245 


mental  stage,  it  has  made  material  advances  in  the  past 
year,  the  300  horse-power  combined  compressor  and  turbine 
being  an  accomplished  fact,  and  a  number  of  120  horse- 
power machines  of  a  special  type  being  actually  installed 
in  submarine  torpedoes  completed  for  active  service. 
When  this  rate  of  progress  is  compared  with  the  time  re- 
quired to  bring  the  reciprocating  gas  engine  to  its  present 
state  of  perfection,  there  appears  to  be  reason  for  encourage- 
ment and  interest. 


WITH 


'    \ 

WITHAIRX 


GAS 


\ 


6000  10000         15000        20000         25000 

FIG.  91. 

The  accompanying  diagram  (Fig.  91)  gives  the  results  of 
practical  tests  of  a  Rateau  multiple  air  compressor,  as  well 
as  a  characteristic  curve  of  the  small  experimental  gas  tur- 
bine of  M.  Armengaud  and  Lemale,  as  communicated  to  the 
author  by  M.  Alfred  Barbezat,  who  has  been  associated 
with  the  late  M.  Rene  Armengaud  in  much  of  his  work. 

Experiments  with  the  large  turbine  and  compressor  have 
shown  the  operative  practicability  of  the  machine,  but  the 


246  THE   GAS   TURBINE. 

consumption  of  petrol  (1200  to  1300  grammes  per  horse- 
power hour)  being  too  high  for  industrial  purposes.  Exper- 
iments which  we  are  not  yet  at  liberty  to  publish,  however, 
indicate  that  the  fuel  consumption  will  be  very  materially 
lowered. 

The  following  data  concerning  gas  turbines  furnished  by 
the  Societe  des  Turbomoteurs  to  the  Creusot  Works  for  use 
in  submarine  torpedoes,  show  the  extent  to  which  the  practi- 
cal development  of  the  gas  turbine  has  already  attained: 

Power 120  horse-power 

Speed 1500  revolutions  per  minute 

Expansion  ratio 8.4  to  1.4  atmospheres  (1:  6) 

Weight  of  turbine 73.16  kilogrammes  (162  Ib.) 

Weight  of  petrol 1.55  kilogrammes  (3.4  Ib.) 

Weight  of  water 11.00  kilogrammes  (24.2) 

Weight  of  air  and  reservoir,  32  + 177  =  209  kilogrammes  (627.6  Ib.) 

'  During  the  past  year  there  has  been  built  in  Paris,  by 
M.  Karavodine,  an  explosion  gas  turbine  developing  about 
2  horse-power,  and  operating  with  regularity  and  success; 
and  from  recent  tests  of  this  machine  by  M.  Alfred  Barbezat 
we  are  able  to  give  some  quantitative  data  concerning  its 
performance. 

The  Karavodine  explosion  gas  turbine  tested  by  M. 
Barbezat  was  provided  with  four  explosion  chambers,  the 
products  of  the  explosions  being  directed  through  four 
separate  nozzles  upon  a  single  turbine  wheel.  This  wheel 
was  of  the  De  Laval  type,  about  6  inches  in  diameter  (150 
centimetres),  carried  upon  a  flexible  shaft,  and  fitted  with 
a  Prony  brake. 

The  general  construction  of  the  explosion  chambers  is 
shown  in  the  illustration.  The  body  of  the  chamber  B  is 
composed  of  cast  iron  and  provided  with  a  water  jacket  A, 
which  does  not  extend  all  the  way  to  the  top,  thus  per- 
mitting the  portion  nearest  the  discharge  nozzle  to  become 
heated.  At  the  lower  end  there  is  provided  an  opening  C 
for  the  entrance  of  the  fuel,  either  gas  or  hydrocarbon  vapor; 


THE    GAS   TURBINE. 


247 


also,  an  opposite  opening  D  for  the  entrance  of  air.  These 
openings  are  both  provided  with  throttle  valves,  not  shown 
in  the  illustration,  by  means  of  which  the  proportions  of 
air  and  gas  may  be  regulated.  At  E  is  an  electric  ignition 
plug,  and  at  F  is  a  plate  steel  valve,  opening  inward,  and 
held  to  its  seat  by  a  spiral  spring  G,  its  lift  being  regulated 
by  a  set-screw  H.  The  discharge  nozzle  is  shown  at  7,  and 
also  a  portion  of  the  perimeter  of  the  turbine  wheel. 


FIG.  92. — Combustion  chamber  of  the  Karavodine  turbine. 

In  starting  the  machine  the  air  opening  D  is  closed  by 
its  throttle  valve  and  a  blast  of  air  is  blown  through  C,  the 
explosive  mixture  being  ignited  by  a  spark  at  E.  After 
the  first  explosion  the  air  entrance  D  is  opened  and  a  sort 
of  pulsometer  action  follows,  thus:  After  each  explosion 
there  follows  a  depression,  or  partial  vacuum,  which  acts 
to  draw  air  and  hydrocarbon  vapor  or  gas  into  the  chamber 
B,  lifting  the  valve  F.  This  mixture  is  instantly  ignited 
by  the  spark  at  E,  and  another  explosion  follows,  to  be 
again  followed  by  another  suction,  and  so  on  indefinitely. 


248 THE    GAS   TURBINE. 

After  a  short  time  the  upper  part  of  the  chamber  B  becomes 
so  hot  that  the  igniter  E  may  be  shut  off,  the  charge  being 
exploded  by  the  heat  of  the  chamber.  The  nozzle  7  is  made 
rather  long,  and  it  is  found  that  the  friction  against  the 
walls  and  the  inertia  of  its  contents  prevent  any  material 
negative  or  back  suction  through  it,  so  that  the  chamber 
B  is  filled  at  every  stroke  almost  entirely  from  the  air  and 
gas  openings  below. 

When  the  tension  on  the  spring  G  and  the  lift  of  the 
valve  F  are  both  carefully  adjusted  this  simple  device  will 
run  for  hours,  without  miss  or  interruption,  the  explosions 
following  each  other  so  closely  as  to  make  practically  a 
continuous  discharge  upon  the  turbine  wheel. 

In  order  to  investigate  the  action  and  pressure  in  this 
explosion  chamber,  a  special  form  of  recording  gauge  was 
made.  The  pressure  in  the  chamber  acted  upon  a  thin 
steel  diaphragm,  of  which  the  deflections  actuated  a  small 
mirror,  throwing  a  beam  of  light  upon  a  rapidly-moving, 
sensitive  film.  The  result  was  the  production  of  a  curve 
of  the  sine  type,  in  which  the  ordinates  represent  pressure 
and  the  abscissae  show  time. 

In  the  diagram  shown  in  the  illustration  the  solid  curved 
line  is  made  up  from  the  average  of  a  number  of  diagrams, 
while  the  dotted  line  shows  the  one  which  deviated  most 
widely  from  the  mean.  During  the  period  A  E  there  was  a 
partial  vacuum  in  the  chamber,  and  the  mixed  charge  was 
drawn  in.  From  E  to  D  the  pressure  of  the  explosion  oc- 
curred, and  the  contents  of  the  chamber  were  discharged 
upon  the  wheel.  The  ignition  began  at  B}  and  the  force  of 
the  explosion  reached  its  maximum  at  C,  while  the  period 
A  B  includes  the  inertia  action  of  the  gases.  The  diagram 
shows  that  a  complete  oscillation  required  0.026  part  of  a 
second,  corresponding  to  between  38  and  39  explosions  per 
second.  The  mean  pressure  A  F  in  the  diagram  was  1.139 
kilogrammes  per  square  centimetre  (absolute),  or  about 


THE    GAS    TURBINE. 


249 


pounds  per  square  inch,  the  maximum  force  of  the  explo- 
sion being  1.345  kilogrammes,  or  about  19  pounds  per  square 
inch.  The  lowest  suction  pressure  was  0.890  kilogramme,  or 
12.6  pounds  absolute,  thus  giving  a  negative  pressure  of 


Alnv- 


O.I 

FIG.  93. — Diagram  of  the  explosion  turbine. 

about  2  pounds  to  draw  the  charge  in,  and  a  discharge  pres- 
sure of  between  4  and  5  pounds  on  the  wheel. 

In  the  machine  tested  by  M.  Barbezat  the  volume  of 
one  chamber  was  230  cubic  centimetres.  Each  nozzle  was 
3  metres  long  and  16  millimetres  bore,  slightly  curved  at 
the  end  to  conform  to  the  shape  of  the  wheel.  The  wheel 


250  THE    GAS   TURBINE. 

itself  was  150  millimetres  in  diameter,  or  5.9  inches,  and 
made  10,000  revolutions  per  minute,  corresponding  to  a 
perimeter  velocity  of  78.5  metres,  or  about  258  feet  per 
second. 

At  the  same  time  the  above  diagrams  were  taken  the 
amount  of  air  drawn  into  the  four  chambers  was  measured 
by  a  meter,  and  the  quantity  of  gasoline  consumed  was 
measured,  while  the  power  developed  was  determined  by 
the  Prony  brake.  The  data  and  results  were  as  follows: 

Air  consumed  per  hour,  62.5  cubic  metres  =  80  kg. 

Gasoline,  6.5  litres  =  4.7  kg. 

Length  of  brake  arm,  46.4  centimetres. 

Weight  on  brake,  248  grammes. 

Speed,  10,000  revolutions  per  minute. 

From  these  figures  the  brake  power  works  out  1.6  horse- 
power, and  as  the  wheel  and  journal  friction  was  determined 
at  0.5  horse-power,  the  actual  indicated  power  was  2.1 
horse-power.  This  gives  a  fuel  consumption  of  2.24  kilo- 
grammes of  gasoline  per  horse-power  hour,  which  is  very 
fair  for  such  a  small  machine,  being  only  about  one-third 
greater  than  that  of  the  old  Lenoir  gas  engine. 

In  considering  the  availability  of  such  a  machine  there 
are  a  number  of  considerations  other  than  the  mere  fuel 
consumption.  The  continuous  turning  effort  is  often  most 
desirable,  and  when  it  is  considered  that  the  wheel  of  this 
machine  was  less  than  6  inches  in  diameter,  the  possibilities 
of  such  an  apparatus  may  become  evident.  The  absence  of 
a  compressor  and  corresponding  reduction  in  weight  and 
size  give  such  a  machine  marked  advantages  over  the 
combustion  turbine,  in  which  the  compressor  is  much  larger 
than  the  turbine  itself,  and  even  if  the  fuel  consumption  is 
as  high  as  indicated  above. 


CHAPTER  VII. 

GENERAL  CONCLUSIONS. 

IN  the  previous  chapters  there  has  been  shown  broadly 
the  mathematical  and  thermodynamical  principles  upon 
which  the  possibilities  of  the  construction  of  a  practicable 
gas  turbine  may  be  based,  together  with  some  account  of 
the  success  which  has  attended  the  design  and  operation 
of  actual  machines.  Much  remains  to  be  done  before  the 
gas  turbine  can  be  expected  to  enter  the  market  in  competi- 
tion with  existing  gas  engines  of  the  reciprocating  type,  but 
there  are  many  active  and  energetic  minds  at  work  upon 
this  portion  of  the  problem,  and  commercial  results  may 
soon  be  expected  to  follow. 

So  far  as  predictions  may  be  made  at  this  stage  of  the 
question,  it  seems  as  if  the  most  immediate  results  are  to 
be  anticipated  from  the  so-called  " mixed"  turbine;  the 
type  in  which  the  injection  of  water  for  cooling  purposes 
causes  the  machine  to  partake  of  the  combined  nature  of 
the  gas  and  the  steam  turbine.  This  is  especially  true  of 
the  combustion  turbine,  in  which  a  continuous  combustion 
in  a  closed  chamber  provides  the  gases  under  pressure  to 
act  upon  the  wheel.  The  turbine  of  the  explosion  type, 
notwithstanding  its  low  thermal  efficiency,  appears  to  have 
arrived  at  a  practical  stage  already,  and  the  machine  con- 
structed by  Karavodine,  and  tested  by  Barbezat,  has 
demonstrated  that  a  dry  gas  turbine  of  this  type  is  an 
operative  machine  already  about  as  efficient  as  a  steam 
engine  of  the  same  capacity. 

Apart  from  the  question  of  thermal  efficiency,  the 
development  of  the  gas  turbine  depends  to  a  large  extent 
upon  other  properties. 

One  of  the  principal  difficulties  with  the  reciprocating 

251 


252  THE    GAS    TURBINE. 

gas  engine  lies  in  the  intermittent  character  of  the  impelling 
forces  upon  the  crank  shaft,  a  defect  which  the  multiplica- 
tion of  cylinders  in  engines  designed  for  automobiles  and 
aeroplanes  is  intended  to  remedy  as  far  as  practicable  with 
machines  of  that  type.  The  continuous  rotary  action  of 
the  turbine  is  such  an  advantage  as  to  outweigh  to  a  large 
degree  its  present  lack  of  fuel  economy.  In  like  manner  the 
high  rotative  speed  lends  itself  to  a  corresponding  reduction 
in  weight  per  unit  of  power,  a  matter  which  closely  con- 
cerns the  development  of  mechanical  flight.  In  this  matter, 
as  in  the  case  of  submarine  propulsion,  fuel  economy  is  a 
secondary  consideration.  The  late  Professor  Langley,  in 
speaking  of  the  engine  of  his  flying  machine,  is  reported  to 
have  said  that  it  might  burn  gold  if  necessary,  so  long  as  it 
fulfilled  all  the  other  requirements  of  the  problem. 

The  development  of  the  rotary  air  compressor  has  an 
important  bearing  upon  the  success  of  the  combustion  tur- 
bine, and  the  work  of  Rateau  in  this  respect  has  shown 
what  may  be  accomplished  by  concentration  upon  such  a 
question.  The  analysis  of  M.  Sekutowicz  shows  the  advan- 
tages of  a  high  degree  of  compression,  and  the  high  efficiency 
of  the  Diesel  motor  is  well  known  to  have  resulted  largely 
from  the  high  compressions  employed  in  that  most  econom- 
ical heat  engine. 

What  is  needed  for  the  further  development  of  the  gas 
turbine,  then,  is  the  experimental  determination  of  the 
data  which  mathematical  analysis  has  shown  to  be  lacking; 
data  concerning  the  behavior  of  gases  in  diverging  nozzles, 
concerning  the  action  of  highly  heated  gases  upon  the 
resistance  of  materials  of  construction,  data  concerning  the 
velocity  of  efflux  from  nozzles,  data  upon  the  practicability 
of  maintaining  extremely  high  rotating  velocities  in  prac- 
tical work. 

Here  is  ample  work  for  the  engineering  laboratories  of 
technical  schools;  work  which  can  be  conducted  with  exist- 


THE    GAS   TURBINE.  253 

Ing  equipment,  and  which  would  form  valuable  contribu- 
tions to  knowledge,  while  at  the  same  time  providing  most 
fruitful  examples  for  instruction  in  the  very  department  of 
engineering  in  which  future  progress  is  to  be  expected,  the 
subject  of  the  manufacture  of  power  and  its  utilization  to 
the  greatest  advantage. 


INDEX 


Academie  des  Sciences,  Tournaire's, 

communication  to,  14-19 
Action  of  heat  on  metals,  86 
Actual  behavior  of  gases  in  nozzles,  222 
Adiabatic   compression,   31,   45,    54, 

123;  133 

efficiency  of,  118 
expansion,  35,  37,  48,  69,  70 

law  of,  112 
flow,  formula  for,  181 
Advantages  of  high  compression,  128» 

148 

of  regenerator,  147 
Aerial  motors,  163 
Air  compressor,  Rateau,  240 
compressors,  197 

efficiency  of,  91 

Analysis  of  mixed  turbines,  156 
Applications  of  the  gas  turbine,  105, 

218 

Armengaud  and  Lemale,  227 
Armengaud     and     Lemale     turbine, 

illustrated,  238 
Armengaud,  Re"ne",  26,  227 
Atkinson,  James:    Discussion  of  Neil- 
son  Paper,  86 
Atomizer  for  gas  turbine,  239 

Banki  motor,  132 
Barber's  turbine,  11-13 
Barbezat,  Alfred,  26,  241 
Barkow,  R.,  8,  27,  121,  130 
Baumann,  A.,  27 
Blades,  losses  in,  191 
Blast  furnace  gases,  176 
Bochet,  A.,  26,  221 
Boulton's  patents,  21,  22 
Bourdon,  M.,  201 
Bourne's  suggestions,  20,  22 
Bray  ton  engine,  31,  32 


Bucholz  turbine,  104 

Burdin,  14,  15,  19 

Burstall,  F.  W.:  Discussion  of  Neil- 
son  Paper,  82 

Butler,  Edward:  Discussion  of  Neil- 
son  Paper,  96 

Carnot's  formula,  29,  91 

cycle,  29,  74,  116 
Cassier's  magazine,  26,  227 
Centrifugal  force,  stresses  due  to,  48 
Circulation  of  cooling  water,  39 
Civil  engineers  of  France:    Discus- 
sion before,  108-221 
Clark,  Ade,  84 

Classification  of  gas  turbines,  191 
Clerk,  Dugald,  30 
Clerk,  Dugald:  Discussion  of  Neilson 

Paper,  97 
Combes,  14 

Combination  cycles,  167 
Combined  gas  and  steam  turbines, 

60-70,  153 

turbines   and    reciprocating   en- 
gines, 102 
Combustible,  influence  of  nature,  176 

mixtures,  207 

Combustion  apparatus,  Davey,  80 
chamber,  Boulton's,  22 
cooling  of,  152 
details  of,  208 
dimensions  of,  209 
injection  of  steam  into,  157 
Lemale,  236 
lining  for,  242 
for  mixed  turbine,  154 
cycles  without  compression,  iso- 

pleric,  137 

experiments  with  Davey  appa- 
ratus, 81 

255 


256 


INDEX. 


Combustion,  isobaric,  124,  144 

nozzle,  de  Laval's,  25 

temperatures,     efficiencies      for 

various,  170 
limitations  of,  152 

turbine,  230 

diagram   for,  231 

under    constant    pressure,    110? 
121 

under  constant  volume,  110 
Comparative  efficiencies,  131 

table  of  cycles,  75 
Compound,  efficiency,  92 
Compression,  adiabatic,   31,  45,   54, 
123,  133 

advantages  of  high,  57, 128,  148, 
221 

efficiency  of  adiabatic,  118 

for  gas  turbines,  83 

isothermal,  68,  127,  135 

work  of,  113 
Compressions,  low,  70 
Compressor,  efficiency  of,  115 

losses,  50 

Rateau,  240 

reciprocating,  6 

rotary,  7,  83 

Strnad,  201 

tests,  201 
Compressors,  air,  51,  197 

efficiency  of,  91 

efficiency  of  rotary,  88 

high-speed,  202 

piston,  197 

rotary,  203 

turbine,  93,  204 
Computations  for  gas  turbine,  213 

for  mixed  turbine,  155 
Conclusions     from     thermodynamic 

study,  169 

Constant  pressure,  combustion  under, 
110,  121 

volume,  combustion  under,  110 
Construction  of  gas  turbines,  details, 
104,  197 


Cool  gases,  injection  of,  151,  164-167 
Cooling  of  combustion  chamber,  152 

of  gas  turbines,  39,  101,  105 

losses,  84 

of  turbine  wheel,  239 

water  circulation  of,  39 
Creusot  works,  246 
Crompton,  Lt.  Col.  R.  E.  B.:    Dis- 
cussion of  Neilson  Paper,  87 
Curves  of  isobaric  cycles,  147 
Cycle,  Carnot,  116 

Diesel,  118 

Ericsson,  142 
Cycles,  Clerk,  30-59 

combination,  167 

comparative  table  of,  75 

curves  of  isobaric,  147 

for  explosion  motors,  133 

gas  turbines,  108,  109 

involving  the  injection  of  water, 
151 

using  heat  regenerators,  142 

using    isobaric    introduction    of 
heat,  121,  144 

using   isopleric    introduction    of 
heat,  133,  150 

using  isothermic  introduction  of 
heat,  116 

table  of  isobaric,  146 

Davey  combustion  chamber,  80 

Davey,  Henry:    Discussion  of  Neil- 
son  Paper,  80 

De  Laval  gas  turbine,  25 

Delaporte,  190 

Deschamps,  J.,  26 

Details  of  gas  turbine  construction, 
104,  197 

Development   methods  for  gas  tur- 
bines, 169 

Diagram  for  combustion  turbine,  231 
explosion,  229 
of  nozzle  sections,  182 
of  nozzle  velocities,  182 

Diesel  cycle,  118 


INDEX. 


257 


Diesel  motor,  31,  52,  53,  83,  132 
Difficulties  with  the  gas  turbine,  83, 

98 
Discharge  from  nozzles,  velocity  of, 

103,  180 
Discs,  efficiencies  of  revolving,  191 

friction  of  revolving,  192 
Discussion  on  Neilson  Paper,  79-107 
Dissociation  in  mixed  turbines,   157 
Divergent  nozzles,  84,  88,  89 
Dowson  gas,  176 

Economy  curves,  gas  turbine,  234 
Efficiencies,  comparative,  131 
compression,  99 
expansion,  99 
of  mixed  turbines,  158 
of  revolving  discs,  191 
for  various  combustion  temper- 
atures, 170 
Efficiency  of  adiabatic  compression, 

118 

of  air  compressors,  91,  115 
compound,  92 
of  gas  turbine,  mechanical,  51, 

109,  112 

of  gas  turbines,  probable,  169 
practical,  75,  220 
of  rotary  compressors,  88 
in  terms  of  temperature  ratio,  114 
thermal,  109 
Elastic-fluid  turbines,  19 
Elements  of  the  gas  turbine  problem, 

108 
Energy  conversion  in  nozzles,  85,  180, 

216 

kinetic,  69 
Engineering  Congress  at  Li£ge,  26 

magazine,  26,  175 

Entropy- temperature    diagrams,    31, 
38,  41,  43,  45,  53,  58,  62,  65,  67,  72 
Ericsson  cycle,  142 
Exhaust  gases  for  operating  turbines, 

100 

under  reduced  pressure,  139 
17 


Expansion,  adiabatic,  35,  37,  48,  69, 

70 

of  air  in  nozzles,  223 
exponent  of,  173-175 
law  of  adiabatic,  112 
in  nozzles,  free,  222 
prolonged     below     atmospheric 

pressure,  138 
temperature,  final,  109 
limitations  of,  163 
Experimental  investigations  needed, 

78 

researches,  214 
turbine,  at  Paris,  232 
Experiments  with  trial  turbine,  233 
Explosion  diagram,  229 
motors,  cycles  for,  133 
turbine,  Karavodine,  247 
applicability  of,  171 
turbines,   54,   56,  57,   171,  228, 

247 

Exponent  of  expansion,  173-175 
variations  of,  174 

Fernihough,  13 

Final  section  of  nozzle,  183 

Flame,  propagation  of,  33,  101,  107, 

209 
Flow  of  gas,  formula  for,  181 

of  gases  through  nozzles,  179 
Fluids,  working,  34 
Formula  of  Saint  Venant,  181 
France,  Discussion  before  the  Society 
of  Civil  Engineers,  108-221 

Societe  des  Ingenieurs  Civils  de, 

26 

Free  expansion  in  nozzles,  222 
Friction  of  discs  revolving  in  air,  192 

losses  in  nozzles,  49,  188-190 
Frictional  losses,  50 
Fuel,  gaseous,  207        9 

liquid,  208 

solid,  207 
Furnace  gases,  176 
Future  of  the  gas  turbine,  217 


258 


INDEX. 


Gardie  producer,  207 
Gas,  Dowson,  176 
engine,  30 

flow  through  nozzles,  179 
formula  for  flow  of,  181 
lean,  176 
regeneration,  206 
and  steam  turbines,  60-70,  153 
turbine,  applications  of,  218 

atomizer  for,  239 

Barber's,  11-13 

Bucholz,  104 

computations  for,  213 

cycles,  30,  108,  109 

De  Laval's,  25 

economy  curves,  234 

future  of,  217 

general  design  of,  212 

large,  244 

mechanical  efficiency  of,  112 

Patschke,  104 

problem,  elements  of,  108 

scheme  of,  6,  7 
turbines,  applications  of,  105 

classification  of,  191 

cooling  of,  101 

details  of  construction,  197 

losses  in,  50 

materials  for,  104 

method  of  development,  169 

pressure  limits  in,  111 

probable  efficiency  of,  169 

regulation  of,  194 

scientific  investigation  into, 
28-79 

small,  76 

for     submarine     torpedoes, 
244 

temperature  limits  in,  110 

water  circulation  in,  39,  101, 

105 

Gaseous  fuel,  207 
mixtures,  177 
Gases,  furnace,  176 

injection  of  cool,  151 


Gases  in  nozzles,  actual  behavior  of, 

222 

velocity  of  discharge,  69,  103 
General  design  of  gas  turbine,  212 
Governing  of  gas  turbines,  194 
Grashof,  187 

Gross  work,  41,  42,  46,  49,  51 
Guide  blades,  16 
Gutermuth,  Prof.,  201 

Hart,  G.,  26,  220 

Heat  balance  for  mixed  turbine,  237 
diagrams,  212 
motors  classified,  227 
regenerators,    cycles   using,    142 
specific,  112 
from  water  jacket,  utilization  of, 

59 
High  compression,  advantages  of,  57, 

128,  148,  221 

High-speed  compressors,  202 
Hot-air  turbine,  Burdin's,  15 
Stolze's,  23,  24 

Influence  of  nature  of  combustible, 

176 

of  temperature  limits,  109 
of  terminal  pressure,  185 
Inge"nieurs  Civils  de  France,  Soci£te 

des,  26 

Initial  cost,  92 
Injection  of  cool  gases,  151 

after  expansion,  163 
at  high  velocity,  166 
at  low  velocities,  164 
of  regenerator  steam,  157 
of  steam,  cycles  using,  151 

after  expansion,  163 
of  water,  cycles  using,  151 

after  expansion,  163 
Institution  of  Mechanical  Engineers, 

28 

Intercooler,  140 
Introduction,  5 

Investigations,  programme  for  future, 
215 


INDEX. 


259 


Isobaric  combustion,  124,  144 
cycles,  curves  of,  147 

table  of,  146 
introduction     of     heat,     cycles 

using,  121,  144 
Isopleric  combustion  cycles  without 

compression,  137 
cycles,  regeneration  with,  150 
introduction  of  heat,  cycles  using, 

133 
Isothermal  compression,  68,  127,  135 

cycles,  partial,  121,  130 
Isothermic     introduction     of     heat, 
cycles  using,  116 

Jets,  velocities  in  steam,  48 
Josse,  Professor,  168 

Karavodine  turbine,  247 
Kinetic  energy,  47,  69,  85 

Lame,  14,  19 

Langen,  Felix,  27 

Laplace,  112 

Large  gas  turbine,  244 

Laval  turbine,  test  of,  223,  224 

Law  of  adiabatic  expansion,  112 

Laws  of  thermodynamics,  112 

Lean  gas,  176 

Lechatelier,  M.,  112 

Lemale,  Charles,  26 

Lemale  combustion  chamber,  236 

Length  of  nozzle,  183 

Leonardo  da  Vinci,  9 

Letombe,  L.,  26,  221 

Liege,  engineering  congress  at,  26 

Limitation  of  temperature  of  com- 
bustion, 152 

Limitations    of   expansion   tempera- 
ture, 163 

Lining  for  combustion  chamber,  242 

Liquid  fuels,  105,  177,  208 

oxygen,  turbines  using,  162 

London,    W.    J.    A.:     Discussion    of 
Neilson  Paper,  100 


Lorenz,  187 

Losses  in  blades,  191 

in  gas  turbines,  50 
Low  compressions,  70 
Lucke,  Charles  E.,  26,  28,  175,  222, 
223 

Martin,  H.  M.:  Discussion  of  Neilson 

Paper,  88 

Materials  for  gas  turbines,  93,  104 
strength  at  high  temperatures, 

211 

Maximum  temperature,  110 
Mechanical  efficiency,  51,  109,  112 
engineers,  institution  of,  28 
features  of  turbines,  179 
Mekarski,  M.,  197 
Metals,  action  of  heat  on,  86 
Mixed  turbines,  60-70,  102,  235 
analysis  of,  156 
combustion  chamber  for,  154 
computations  for,  155 
dissociation  in,  157 
efficiencies  of,  158 
heat  balance  for,  237 
table  of,  160 
Morin,  14,  19 

Moss,  Dr.  Sanford  A.,  7,  26 
Motor  losses,  50 

Multiple  turbines,  Tournaire's,  15 
Murdock,  11 

Nature  of  combustible,  influence  of, 

176 
Negative  work,  36,  41,  42,  49,  51,  83, 

85 

Neilson,  R.  M.,  26,  28-79,  93 
Nozzle,  final  section  of,  183 
length  of,  183 
sections,  diagram  of,  182 

ratio  of,  184 

velocities,  diagram  of,  182 
velocity  in  neck  of,  184 
Nozzles,  actual  behavior  of  gases  in, 
222 


260 


INDEX. 


Nozzles,  combination,  89 
construction  of,  210 
diverging,  84,  89 
energy  delivered  from,  180 

of  gases  in,  216 
expansion  of  air  in,  223 
experiments  with,  85 
flow  of  gases  through,  179 
free  expansion  in,  222 
friction  losses  in,  188-190 
oscillations  in,  90,  95,  186-188 
rotating,  49 
shock  in,  187 

Stodola's  experiments  with,  88 
temperature  drop  in,  222 

measurements    in,  215 
velocities  in,  85 
velocity  of  discharge  from,  180 

Oscillations  in  nozzles,  90,  95 
Otto  cycle,  30 

Oxidation  of  turbine  blades,  211 
Oxygen,  turbines  using  liquid,  162 

Parallel  flow  turbine,  56 

Parsons's  patent,  24 

Parsons  turbine,  33 

Partial  isothermal  cycles,  121 

Patschke  turbine,  104 

Piston  compressors,  197 

Poisson,  112 

Poisson's  law,  173 

Poncelet,  14,  19 

Power  regulation  of  turbines,  77 

Practical  efficiency,  75 

Prandtl,  187 

Pressure  limits  in  gas  turbines,  111 

volume  diagrams,  31,  38,  40,  42, 
44,  52,  58,  61,  63,  66,  71 

waves  in  nozzles,  90,  186,  188 
Probable  efficiency  of  gas  turbines,  169 
Proell,  187 

Programme  for  future  investigations, 
215 


Prolonged  expansion,  138 
Propagation    of    flame,    velocity    of, 
101,  107 

Radiation  losses,  50 
Rateau  air  compressor,  240 
Ratio  of  nozzle  sections,  184 
Rayleigh,  187 
Reeve,  Sidney  A.,  26 
Reduced  pressure  exhaust,  139 
Regeneration  from  gas  to  gas,  206 

with  isopleric  cycles,  150 

by  steam,  206 

of  waste  heat,  145 
Regenerator,  70-73 

action,  table  of,  149 

advantages  of,  147 

cycles  using  heat,  142 

design,  161 

steam,  injection  of,  157 

thermal,  205 

Regulation  of  gas  turbines,  77,  194 
Revolving  discs,  efficiencies  of,  191 

friction  of,  192 

wheels,  construction  of,  211 
Rey,  Jean,  26,  219 
Rich  fuel  with  water  injection,  162 
Rotary  compressors,  83,  203 
Rotating  nozzles,  49 

Saint  Venant,  formula  of,  181 
Sautter,  Harle  and  Co.,  219 
Scheme  of  gas  turbine,  6,  7 
Schweizerische  Bauzeitung,  26 
Scott,    E.    Kilburn:     Discussion    of 

Neilson  Paper,  103 
Section  of  nozzle,  final,  183 
Seguier,  14 
Sekutowicz,  L.,  26 
Sekutowicz,  L.,  Paper  by,  108-218 
Shock  in  nozzles,  187 
Small  gas  turbines,  76 
Smith,    Robert    H.:     Discussion    of 

Neilson  Paper,  90 
Smoke  jack,  9-11 


INDEX. 


261 


Societe    des    Ingeriieurs    Civils    de 

France,  26 

Societe  des  Turbomoteurs,  224,  245 
Specific  heat,  34,  112 
Steam,  cycles  using  injection  of,  151 
and  gas  turbine,  60-70,  153 
injection  after  expansion,  163 

of  regenerator,  157 
jets,  velocities  in,  48 
regeneration  by,  206 
Stodola,  A.,  88,  164,  187,  189,  190 
Stodola,  experiments  with  divergent 

nozzles,  88 

Stodola's  experiments  with  jets,  94 
Stolze,  hot  air  turbine,  23,  24 
Strength  of  materials  at  high  tem- 
peratures, 211 
Strnad  compressor,  201 
Structural  difficulties  with  turbines, 

220 
Submarine  motors,  163 

torpedoes,  gas  turbines  for,  24 
Suction  gas  for  turbines,  77 
Sulphur  dioxide  turbine,  140 

Table  of  mixed  turbines,  160 

of    regeneration    with    isopleric 

cycles,  151 

Temperature  of  combustion,  limita- 
tions of,  152 

drop  in  nozzles,  222 

of  expansion,  109 

limitations  of  expansion,  163 

limits,  influence  of,  109 

maximum,  110 

measurements  in  nozzles,  215 

ratio  in  terms  of  efficiency,  114 
Temperatures,  efficiencies  for  various 
combustion,  170 

in  gas  turbines,  86 

practicable,  33,  37,  39 
Terminal  pressure,  influence  of,  185 
Tests  of  compressors,  201 

of  explosion  turbine,  248 
Thermal  efficiency,  109 


Thermal  regenerators,  205 
Thermodynamic  study,  169 
Thermodynamics,  laws  of,  112 
Torpedoes,    gas    turbines    for    sub- 
marine, 244 
Tournaire,  14,  19 

Trial  turbine,  experiments  with,  233 
Turbine,  applications  of  the  gas,  218 
atomizer  for  gas,  239 
combustion,  230 
combustion  chamber  for  mixed, 

236 

compressor  at  Bethume,  219 
compressors,  93,  204,  219 
computations  for  gas,  213 
construction,  material  for,  93 
economy  curves  of  gas,  234 
experiments  with  trial,  233 
future  of  the  gas,  217 
general  design  of  gas,  212 
heat  balance  for  mixed,  237 
Karavodine  explosion,  248 
parallel  flow,  56 
at  Paris,  experimental,  232 
practical  efficiency  qf,  220 
waste  heat,  167 
wheels,  construction  of,  211 
Turbines,    computation    for    mixed, 

155-158 

efficiencies  of  mixed,  158 
elastic  fluid,  19 
explosion,  54,  56,  57,  228 
using  gas  and  steam,  60-70 
liquid  fuel  for,  106 
using  liquid  oxygen,  162 
mechanical  features  of,  179 
mixed,  235 

operated  with  exhaust  gases,  100 
for  submarine  torpedoes,  244 
table  of  mixed,  160 
uncooled,  55 
Turbomoteurs,  Socie"te*  des,  26, 224, 245 

Uncooled  turbines,  33,55 
Utilization  of  heat  from  water  jacket, 
59 


262 


INDEX. 


Velocities  in  nozzles,  85 

in  steam  jets,  48 

Velocity  of  discharge  from  nozzles, 
103,  180 

of  gases,  69 

in  neck  of  nozzle,  184 

of    propagation    of    flame,    101, 

107 

Vermand,  M.,  173 
Vinci,  Leonardo  da,  9 

Waste  heat  recovery,  140 

turbine,  167 
Water  circulation  in  gas  turbines,  39, 

101,  105 

injection,  cycles  using,  151 
after  expansion,  163 
with  rich  fuel,  162 


Water  jacket,  utilization  of  heat  from 

59 
siphons  for  gas  turbines,  97 

Waves  in  nozzles,  pressure,  90, 186, 188 

Weber,  187 

Wegener,  Richard,  27 

Wheel,  water  cooling  for,  239 

Wheels,  construction  of,  211 

Wilkins,  Bishop,  9,  10 

Windmill  as  a  gas  turbine,  9 

Witz,  M.  A.,  112 

Work  of  compression,  113 
gross,  41,  42,  46,  49,  51 
negative,  36,  41,  42,  49,  51 

Working  fluids,  34 

Zeitschrift  fiir  des  Gesamte  turbin- 
enwesen,  27 


UNIVERSITY  OF  CALIFORNIA  LIBRARY 
BERKELEY 

Return  to  desk  from  which  borrowed. 
This  book  is  DUE  on  the  last  date  stamped  below 


LD  21-100m-9,'48(B399sl6)476 


YC  33383 


793334 

TOY 


Engineering 
Library 

UNIVERSITY  OF  CALIFORNIA  LIBRARY 


